fix(ci): pin cargo version in release-proposal-test.yml

[iunanua]

What does this PR do?

Pin cargo version to fix problems with cargo package after setting rust version 1.87.0 in rust-toolchain.toml

[datadog-datadog-prod-us1-2]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 72.92% (+0.04%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 5be7957 | Docs | Datadog PR Page | Give us feedback!}

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.92%. Comparing base (1fb8aca) to head (5be7957).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2059      +/-   ##
==========================================
+ Coverage   72.88%   72.92%   +0.03%     
==========================================
  Files         460      460              
  Lines       76463    76463              
==========================================
+ Hits        55731    55759      +28     
+ Misses      20732    20704      -28     

Components	Coverage Δ
libdd-crashtracker	65.36% <ø> (-0.03%)	⬇️
libdd-crashtracker-ffi	36.82% <ø> (ø)
libdd-alloc	98.77% <ø> (ø)
libdd-data-pipeline	85.65% <ø> (ø)
libdd-data-pipeline-ffi	76.17% <ø> (ø)
libdd-common	79.89% <ø> (ø)
libdd-common-ffi	74.41% <ø> (ø)
libdd-telemetry	73.34% <ø> (ø)
libdd-telemetry-ffi	31.36% <ø> (ø)
libdd-dogstatsd-client	82.64% <ø> (ø)
datadog-ipc	76.22% <ø> (+1.46%)	⬆️
libdd-profiling	81.69% <ø> (ø)
libdd-profiling-ffi	64.79% <ø> (ø)
libdd-sampling	97.46% <ø> (ø)
datadog-sidecar	29.19% <ø> (ø)
datdog-sidecar-ffi	10.17% <ø> (ø)
spawn-worker	48.86% <ø> (ø)
libdd-tinybytes	93.80% <ø> (ø)
libdd-trace-normalization	81.71% <ø> (ø)
libdd-trace-obfuscation	87.30% <ø> (ø)
libdd-trace-protobuf	68.25% <ø> (ø)
libdd-trace-utils	88.94% <ø> (ø)
libdd-tracer-flare	86.88% <ø> (ø)
libdd-log	74.83% <ø> (ø)

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[dd-octo-sts]

Artifact Size Benchmark Report

aarch64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.so	7.63 MB	7.63 MB	0% (0 B) 👌
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.a	82.94 MB	82.94 MB	0% (0 B) 👌

aarch64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.so	10.25 MB	10.25 MB	0% (0 B) 👌
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.a	94.03 MB	94.03 MB	0% (0 B) 👌

libdatadog-x64-windows

Artifact	Baseline	Commit	Change
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.dll	24.53 MB	24.53 MB	0% (0 B) 👌
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.lib	83.96 KB	83.96 KB	0% (0 B) 👌
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.pdb	178.26 MB	178.25 MB	-0% (-16.00 KB) 👌
/libdatadog-x64-windows/debug/static/datadog_profiling_ffi.lib	915.33 MB	915.33 MB	0% (0 B) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.dll	8.03 MB	8.03 MB	0% (0 B) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.lib	83.96 KB	83.96 KB	0% (0 B) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.pdb	23.77 MB	23.77 MB	0% (0 B) 👌
/libdatadog-x64-windows/release/static/datadog_profiling_ffi.lib	47.43 MB	47.43 MB	0% (0 B) 👌

libdatadog-x86-windows

Artifact	Baseline	Commit	Change
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.dll	21.27 MB	21.27 MB	0% (0 B) 👌
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.lib	85.29 KB	85.29 KB	0% (0 B) 👌
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.pdb	182.23 MB	182.23 MB	-0% (-8.00 KB) 👌
/libdatadog-x86-windows/debug/static/datadog_profiling_ffi.lib	908.49 MB	908.49 MB	0% (0 B) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.dll	6.20 MB	6.20 MB	0% (0 B) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.lib	85.29 KB	85.29 KB	0% (0 B) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.pdb	25.48 MB	25.48 MB	0% (0 B) 👌
/libdatadog-x86-windows/release/static/datadog_profiling_ffi.lib	45.08 MB	45.08 MB	0% (0 B) 👌

x86_64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.a	73.95 MB	73.95 MB	0% (0 B) 👌
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.so	8.52 MB	8.52 MB	0% (0 B) 👌

x86_64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.a	89.36 MB	89.36 MB	0% (0 B) 👌
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.so	10.36 MB	10.36 MB	0% (0 B) 👌