Add a step that forces the fetch of the specific commit

This will fetch even if the commit is on a PR from a fork

lib/spack/spack/fetch_strategy.py

@@ -862,6 +862,9 @@ def clone(self, dest=None, commit=None, branch=None, tag=None, bare=False):
                 )
 
             with working_dir(dest):
+                # By defaults, on all references are fetched by the clone
+                fetch_args = ["fetch", "origin", "--depth 1", commit]
+                git(*fetch_args)
                 checkout_args = ["checkout", commit]
                 if not debug:
                     checkout_args.insert(1, "--quiet")