test: update merge_config expectations for nbviewer.jupyter.org default

[blink1073]

Fixes the failing Test merge_config.py job by updating test fixtures to include the ^https://nbviewer.jupyter.org/ default pattern added in 8c6bcbe.

[greptile-apps]

Confidence Score: 5/5

[Low impact] This test-only correction appears safe to merge.

Summary

Updated test_merge_config.sh to expect the existing ^https://nbviewer.jupyter.org/ default.

• Config tests now expect the nbviewer Jupyter default.

_{Reviews (1) · Last reviewed commit: "test: update merge_config expectations f..." · Reviewed by Greptile}