[CI] Fix SemVer check base commit

.github/scripts/generate-prdoc.py

@@ -96,6 +96,7 @@ def create_prdoc(pr, audience, title, description, patch, bump, force):
 	# write the parsed PR documentation back to the file
 	with open(path, "w") as f:
 		yaml.dump(prdoc, f)
+		print(f"PrDoc for PR {pr} written to {path}")
 
 def parse_args():
 	parser = argparse.ArgumentParser()

.github/workflows/check-semver.yml

@@ -12,22 +12,21 @@ concurrency:
 env:
   TOOLCHAIN: nightly-2024-06-01
 
-
 jobs:
   check-semver:
     runs-on: ubuntu-latest
     container:
       image: docker.io/paritytech/ci-unified:bullseye-1.77.0-2024-04-10-v20240408
     steps:
       - uses: actions/checkout@692973e3d937129bcbf40652eb9f2f61becf3332 # v4.1.7
+        with:
+          fetch-depth: 2
 
       - name: extra git setup
-        env:
-          BASE: ${{ github.event.pull_request.base.sha }}
         run: |
           git config --global --add safe.directory '*'
-          git fetch --no-tags --no-recurse-submodules --depth=1 origin $BASE
-          git branch old $BASE
+
+          git branch old HEAD^1
 
       - name: Comment If Backport
         if: ${{ startsWith(github.event.pull_request.base.ref, 'stable') }}