.copr/Makefile: Allow building RPM without git remote

The Prow CI build job we have doesn't seem to keep the git remote
around.

.copr/Makefile

@@ -2,8 +2,9 @@ srpm:
 	./ci/installdeps.sh
 	# similar to https://github.com/actions/checkout/issues/760, but for COPR
 	git config --global --add safe.directory '*'
-	# fetch tags so `git describe` gives a nice NEVRA when building the RPM
-	git fetch origin --tags
+	# if we have a git repo with remotes, fetch tags so `git describe` gives a nice NEVRA when
+	# building the RPM
+	if git remote | grep origin; then git fetch origin --tags; fi
 	git submodule update --init --recursive
 	# Our primary CI build goes via RPM rather than direct to binaries
 	# to better test that path, including our vendored spec file, etc.