Don't print the exact same warning twice

In the step output, the warning that produces a workflow annotation
is fully readable (and even made to stand out), so it doesn't need
to be printed in the plain way as well, which can be reserved for
when GitHub Actions is not detected.

Author: EliahKagan

Diff for: init-tests-after-clone.sh

@@ -14,10 +14,10 @@ no_version_tags() {
 }
 
 warn() {
-    printf '%s\n' "$@" >&2  # Warn in step output.
-
     if test -n "${GITHUB_ACTIONS-}"; then
         printf '::warning ::%s\n' "$*" >&2  # Annotate workflow.
+    else
+        printf '%s\n' "$@" >&2
     fi
 }