[CI] restrict benchmarks to 8.10.3

Author: pepeiborra

.github/workflows/bench.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ghc: ['8.10.2', '8.8.4']
+        ghc: ['8.10.3']
         os: [ubuntu-latest]
 
     steps: