chore: CI: pin specific commit for pbrt/ocaml-protoc

Author: c-cube

.github/workflows/main.yml

@@ -42,8 +42,7 @@ jobs:
           allow-prerelease-opam: true
 
       - run: |
-          opam pin ocaml-protoc 3.0.1 -y -n
-          opam pin pbrt 3.0.1 -y -n
+          opam pin https://github.com/mransan/ocaml-protoc.git#ea37bad918adc6c07a5437175763b32e2cab54ae --dev -y -n
           opam install pbrt -y
 
       # We cannot install packages that need eio on ocaml versions before 5