test(s3): address review feedback on the versioning suite (#9846)

- Different-users bucket test: use getNewBucketName() so the bucket carries the
  tracked prefix and run id and gets swept if the test leaks, instead of an
  untracked name.
- Makefile: clarify that '.' matches the opt-in stress tests but they self-skip
  without ENABLE_STRESS_TESTS, so they don't execute in the default run.
- Versioned list test: guard the Object.Size dereference with require.NotNil.

test/s3/versioning/Makefile

@@ -12,8 +12,8 @@ FILER_PORT := 8888
 TEST_TIMEOUT := 10m
 # Run every test in the suite by default. "TestVersioning" used to leave whole
 # tests (bucket creation, suspended delete, directory/version listing) ungated.
-# Opt-in stress tests self-skip without ENABLE_STRESS_TESTS and run in their own
-# targets, so "." does not pull them in here.
+# Opt-in stress tests are matched by "." but self-skip without ENABLE_STRESS_TESTS
+# (they run with it set in their own targets), so they don't actually execute here.
 TEST_PATTERN := .
 
 .DEFAULT_GOAL := help

test/s3/versioning/s3_bucket_creation_test.go

@@ -135,7 +135,8 @@ func TestBucketCreationBehavior(t *testing.T) {
 // (versus BucketAlreadyOwnedByYou for the owner re-creating it).
 func TestBucketCreationWithDifferentUsers(t *testing.T) {
 	ctx := context.Background()
-	bucketName := "test-different-users-" + fmt.Sprintf("%d", time.Now().UnixNano())
+	// Tracked prefix + run id so cleanupAllTestBuckets sweeps it if the test leaks.
+	bucketName := getNewBucketName()
 
 	// User A owns the bucket.
 	clientA := getS3Client(t)

test/s3/versioning/s3_directory_versioning_test.go

@@ -681,6 +681,7 @@ func TestVersionedObjectListBehavior(t *testing.T) {
 	assert.NotContains(t, *listedObject.Key, versionId, "Object key should not contain version ID")
 
 	// Verify object properties
+	require.NotNil(t, listedObject.Size, "Object size should not be nil")
 	assert.Equal(t, int64(len(content)), *listedObject.Size, "Object size should match")
 	assert.NotNil(t, listedObject.ETag, "Object should have ETag")
 	assert.NotNil(t, listedObject.LastModified, "Object should have LastModified")