fix: Replace pytz with stdlib datetime.timezone and zoneinfo (#5863)

[sagemaker-bot]

Description

Replaces pytz usage with Python stdlib datetime.timezone.utc and zoneinfo.ZoneInfo in sagemaker.workflow.pipeline and sagemaker.workflow.triggers. This eliminates the undeclared pytz dependency that causes ModuleNotFoundError when pandas>=3 removes its transitive pytz dependency.

Related Issue

Fixes #5863

Changes Made

• src/sagemaker/workflow/pipeline.py — replaced pytz.utc with datetime.timezone.utc
• src/sagemaker/workflow/triggers.py — replaced pytz.timezone() with zoneinfo.ZoneInfo()
• tests/unit/sagemaker/workflow/test_triggers.py — updated tests to use zoneinfo

AI-Generated PR

This PR was generated and validated by the PR Generator Sandbox. The sandbox:

1. Generated the fix using Bedrock Agent
2. Caught a test failure (.localize() not available on ZoneInfo) and auto-fixed it
3. Passed the full V2 test suite (unit + integ)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.15%. Comparing base (a140cfc) to head (b752fec).
⚠️ Report is 26 commits behind head on master-v2.

Additional details and impacted files

@@              Coverage Diff              @@
##           master-v2    #5917      +/-   ##
=============================================
+ Coverage      86.07%   86.15%   +0.08%     
=============================================
  Files            455      455              
  Lines          44414    44672     +258     
=============================================
+ Hits           38229    38488     +259     
+ Misses          6185     6184       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.