test: configure git in browser tests workflow

[avi-alpert]

Description

Fix workflow failure: https://github.com/aws/agentcore-cli/actions/runs/25002886488/job/73219242607

Add the missing Configure git step to the browser-tests CI job. agentcore create runs git init + git commit internally, which fails on GitHub Actions runners that don't have a git identity configured.

This was missed when splitting browser tests into their own job in #975 — the e2e job had this step but it wasn't carried over.

Related Issue

Follow-up to #975

Documentation PR

N/A

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

• Verified the step is identical to the one in the e2e job

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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