Fetch base ref explicitly in test jobs for targeted diff

fetch-depth: 0 fetches the PR branch history but the base SHA may not
be reachable. Explicitly fetch the base ref so the diff works.
Signed-off-by: Gregor Zeitlinger <gregor.zeitlinger@grafana.com>

Author: zeitlinger

.github/workflows/build-common.yml

@@ -314,6 +314,10 @@ jobs:
           # Need history for determine-affected-tests.sh to diff against base
           fetch-depth: ${{ needs.determine-affected.outputs.build-scope == 'TARGETED' && 0 || 1 }}
 
+      - name: Fetch base ref for targeted diff
+        if: ${{ needs.determine-affected.outputs.build-scope == 'TARGETED' }}
+        run: git fetch origin "${{ inputs.pr-base-sha }}"
+
       - name: Free disk space
         run: .github/scripts/gha-free-disk-space.sh
 

.github/workflows/reusable-test-latest-deps.yml

@@ -61,6 +61,10 @@ jobs:
         with:
           fetch-depth: ${{ needs.determine-affected.outputs.build-scope == 'TARGETED' && 0 || 1 }}
 
+      - name: Fetch base ref for targeted diff
+        if: ${{ needs.determine-affected.outputs.build-scope == 'TARGETED' }}
+        run: git fetch origin "${{ inputs.pr-base-sha }}"
+
       - name: Free disk space
         run: .github/scripts/gha-free-disk-space.sh