ci(nopin): pinning is very slow and not necessary

We do not publish or use the opam packages from this repo,
and therefore pinning is unnecessary.
'opam install --deps-only --with-test .' works without pinning on the version of 'opam' we have here.

Pinning ~71 packages is very slow since it makes a full copy of the source+.git folder every time.
Skip pinning, this also saves a few gigabytes of disk space.
This also makes the cleanup-xapi-environment action a no-op.

For testing the correctness of opam packages:
* we still have the xs-opam CI
* we can introduce opam-dune-lint that statically checks opam and dune for missing dependencies (needs new release first)

Signed-off-by: Edwin Török <[email protected]>

.github/workflows/setup-xapi-environment/action.yml

@@ -66,6 +66,7 @@ runs:
         ocaml-compiler: ${{ steps.dotenv.outputs.ocaml_version_full }}
         opam-repositories: |
           xs-opam: ${{ steps.dotenv.outputs.repository }}
+        opam-pin: false
         dune-cache: true
 
     - name: Install dependencies