ci: deepen PR branch history for Scalpel merge-base detection

The checkout at depth=1 means the merge base between the PR and
the base branch is unreachable. Add git fetch --deepen=200 to
make the PR branch history available alongside the base branch.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: gnodet

.github/workflows/pr-build-main.yml

@@ -80,8 +80,9 @@ jobs:
       - name: Fetch base branch for Scalpel change detection
         if: ${{ !inputs.skip_full_build }}
         run: |
-          # Scalpel needs the base branch to detect changes.
-          # git CLI handles shallow clones reliably (JGit's fetchSubmodules does not).
+          # Scalpel needs the merge base between HEAD and the base branch.
+          # The checkout is depth=1, so deepen both sides for merge-base reachability.
+          git fetch --deepen=200 2>/dev/null || true
           git fetch --no-tags --depth=200 origin "${GITHUB_BASE_REF:-main}:refs/remotes/origin/${GITHUB_BASE_REF:-main}"
       - id: install-packages
         uses: ./.github/actions/install-packages

.github/workflows/sonar-build.yml

@@ -45,6 +45,7 @@ jobs:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
       - name: Fetch base branch for Scalpel change detection
         run: |
+          git fetch --deepen=200 2>/dev/null || true
           git fetch --no-tags --depth=200 origin "${GITHUB_BASE_REF:-main}:refs/remotes/origin/${GITHUB_BASE_REF:-main}"
       - id: install-packages
         uses: ./.github/actions/install-packages