Increase fetch-depth buffer in manual-benchmark.yml (#7363)

Author: zeme-wana

.github/workflows/manual-benchmark.yml

@@ -29,8 +29,10 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4.3.0
         with:
-          # We need at least one commit before master to compare against
-          fetch-depth: 5
+          # It's possible that new commits get merged into master since the PR 
+          # was opened. We need a safe buffer to make sure that our use of merge-head 
+          # leter always finds the true parent of the first PR commit.
+          fetch-depth: 100
 
       - name: React With Rocket 
         uses: actions/github-script@v7.1.0

scripts/ci-plutus-benchmark.sh

@@ -60,6 +60,7 @@ echo "[ci-plutus-benchmark]: Running benchmark for PR branch at $PR_BRANCH_REF .
 2>&1 cabal bench "$BENCHMARK_NAME" | tee bench-PR.log
 
 echo "[ci-plutus-benchmark]: Switching branches ..."
+# merge-base finds the fork point, which is the true parent of the first PR commit.
 git checkout "$(git merge-base HEAD origin/master)"
 BASE_BRANCH_REF=$(git rev-parse --short HEAD)