gha: use stable version of golang in CI

benchstat@latest became incompatible with the go version 1.20 from
go.mod. Instead of using what's inside go.mod, use latest stable.
Inside go.mod I want to keep as old as possible go version as to not
cause trouble to users with older installs.

Author: gabriel-vasile

.github/workflows/benchmark.yml

@@ -18,15 +18,17 @@ jobs:
     - name: Install Go
       uses: actions/[email protected]
       with:
-        go-version-file: 'go.mod'
+        go-version: 'stable'
+    - run: go install golang.org/x/perf/cmd/benchstat@latest
 
     # 30 runs with 100ms benchtime seems to result in acceptable p-values
     # When I tried with count=10, it would be unreliable because of the actions
     # runner is in a shared environment and CPU and mem would be affected by others. (or so I think)
     - run: go test -run=none -bench=. -count=30 -benchtime=100ms -timeout=20m > /tmp/prev
+
     - name: Checkout code
       uses: actions/[email protected]
+    # Second run of benchmarks
     - run: go test -run=none -bench=. -count=30 -benchtime=100ms -timeout=20m > /tmp/curr
 
-    - run: go install golang.org/x/perf/cmd/benchstat@latest
     - run: benchstat /tmp/prev /tmp/curr