ci: update nightly version description

With the addition of the config module, the output of `git describe` can
look odd without restricting to clair's tags.

Signed-off-by: Hank Donnay <hdonnay@redhat.com>

.github/script/nightly-module.sh

@@ -12,4 +12,4 @@ git diff
 test -d vendor && rm -rf vendor
 go mod tidy
 go mod vendor
-printf '::set-output name=clair_version::%s\n' "$(git describe --tags --always --dirty)"
+printf '::set-output name=clair_version::%s\n' "$(git describe --tags --always --dirty --match 'v4.*')"