Fix benchmark that does not compare the exact result from the previous commit

.github/workflows/benchmark.yml

@@ -24,7 +24,15 @@ jobs:
         uses: actions/cache@v4
         with:
           path: ./benchmarks
-          key: ${{ runner.os }}-benchmark
+          # Use the current commit SHA as the cache key.
+          # This key won't exist on the first run, so the cache match falls back to restore-keys.
+          # Though, it won't be matched, the cache created will use this key as the cache key.
+          # So the next commit will be able to restore this cache (from the restore-keys).
+          # https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/caching-dependencies-to-speed-up-workflows#matching-a-cache-key
+          key: ${{ runner.os }}-benchmark-${{ github.sha }}
+          # `github.event.before` means the commit before the push (i.e. the previous commit).
+          # So we can fetch the exact benchmark data from the previous commit.
+          restore-keys: ${{ runner.os }}-benchmark-${{ github.event.before }}
       - name: Store benchmarks result
         uses: benchmark-action/[email protected]
         with: