fix(melange): build time benchmarks (#12053)

Signed-off-by: Antonio Nuno Monteiro <[email protected]>

Author: anmonteiro

.github/workflows/bench.yml

@@ -5,7 +5,6 @@ on:
   push:
     branches:
       - main
-      - ci-bench/fix-after-ocaml51
 
 permissions:
   # deployments permission to deploy GitHub pages website
@@ -85,6 +84,7 @@ jobs:
       - name: Install all deps
         working-directory: pupilfirst
         run: |
+          opam pin add --no-action .
           opam install -y . --deps-only
 
       - name: Run pupilfirst benchmark