Optimize git clone performance by using shallow-since instead of full history (#432)

Replace --deepen=2147483647 with --shallow-since="6 months ago" to improve clone performance while maintaining sufficient commit history for gitStream analysis.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude <[email protected]>

Author: MishaKav

action.yml

@@ -126,12 +126,11 @@ runs:
       if: ${{ env.SHOULD_CHECKOUT == 'true' }}
       shell: bash
       run: |
-        ALL=2147483647
         cd gitstream && cd repo
         git config checkout.defaultRemote origin
-        git fetch --deepen=$ALL origin $'${{ steps.safe-strings.outputs.base_ref }}'
+        git fetch --shallow-since="6 months ago" origin $'${{ steps.safe-strings.outputs.base_ref }}'
         git remote add upstream $'${{ steps.safe-strings.outputs.url }}'
-        git fetch --deepen=$ALL upstream $'${{ steps.safe-strings.outputs.head_ref }}'
+        git fetch --shallow-since="6 months ago" upstream $'${{ steps.safe-strings.outputs.head_ref }}'
         git checkout -b $'upstream/${{ steps.safe-strings.outputs.head_ref}}' $'upstream/${{ steps.safe-strings.outputs.head_ref}}'
         git checkout $'${{ steps.safe-strings.outputs.base_ref }}'
         git checkout $'${{ steps.safe-strings.outputs.head_ref }}'