test(ci): skip chmod-dependent tests when running as root

Docker CI containers run as root by default (golang:1.26-alpine), where
os.Chmod has no effect and permission restrictions don't apply. Four
tests were failing because they relied on chmod to force error paths:

- gradle: TestWriteVersionReadOnly
- cmd:    TestInitConfigWriteFails, TestRunLatestTagFails
- gitutil: TestLatestTagTagsIterFails (had broken skip logic that only
  fired if Chmod itself errored, which never happens as root)

Replace all four with an upfront os.Getuid() == 0 check so they are
skipped cleanly in root environments and still run (and must pass) on
non-root local development.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/main_test.go

@@ -852,6 +852,9 @@ func TestPrintVerboseConfigDirect(t *testing.T) {
 // ── initConfig coverage ───────────────────────────────────────────────────────
 
 func TestInitConfigWriteFails(t *testing.T) {
+	if os.Getuid() == 0 {
+		t.Skip("skipping: chmod restrictions do not apply when running as root")
+	}
 	dir := t.TempDir()
 	os.Chmod(dir, 0555)
 	defer os.Chmod(dir, 0755)
@@ -904,6 +907,9 @@ func TestRunWorkingTreeCheckFails(t *testing.T) {
 }
 
 func TestRunLatestTagFails(t *testing.T) {
+	if os.Getuid() == 0 {
+		t.Skip("skipping: chmod restrictions do not apply when running as root")
+	}
 	_, dir := setupRepo(t)
 	addFile(t, dir, "x.go", "// fix")
 	repo, _ := gogit.PlainOpen(dir)