fix(cli): serialize TestUseKeyring subtests to avoid OS keyring flakes (#25924)

`TestUseKeyring/Logout` flaked on Windows in CI: after `coder logout`
returned `nil`, `env.keyring.Read(env.clientURL)` still returned the
credential instead of `os.ErrNotExist`. The CI logs showed the logout
HTTP call succeeded and the keyring service name and server URL were
correct.

The OS keyring is shared global state on Windows and macOS, and
concurrent in-process access seems to produce intermittent failures on
Windows (ERROR_NOT_FOUND, stale reads after delete). This change
serializes TestUseKeyring subtests in an attempt to fix the intermittent
failures. The root cause is unknown.

Generated with assistance by Coder Agents

cli/keyring_test.go

@@ -55,14 +55,12 @@ func setupKeyringTestEnv(t *testing.T, clientURL string, args ...string) keyring
 	return keyringTestEnv{serviceName, backend, inv, cfg, parsedURL}
 }
 
+//nolint:paralleltest,tparallel // Windows OS keyring has intermittent failures with concurrent access
 func TestUseKeyring(t *testing.T) {
 	// Verify that the --use-keyring flag default opts into using a keyring backend
 	// for storing session tokens instead of plain text files.
-	t.Parallel()
 
 	t.Run("Login", func(t *testing.T) {
-		t.Parallel()
-
 		if runtime.GOOS != "windows" && runtime.GOOS != "darwin" {
 			t.Skip("keyring is not supported on this OS")
 		}
@@ -109,8 +107,6 @@ func TestUseKeyring(t *testing.T) {
 	})
 
 	t.Run("Logout", func(t *testing.T) {
-		t.Parallel()
-
 		if runtime.GOOS != "windows" && runtime.GOOS != "darwin" {
 			t.Skip("keyring is not supported on this OS")
 		}
@@ -174,8 +170,6 @@ func TestUseKeyring(t *testing.T) {
 	})
 
 	t.Run("DefaultFileStorage", func(t *testing.T) {
-		t.Parallel()
-
 		if runtime.GOOS != "linux" {
 			t.Skip("file storage is the default for Linux")
 		}
@@ -220,8 +214,6 @@ func TestUseKeyring(t *testing.T) {
 	})
 
 	t.Run("EnvironmentVariable", func(t *testing.T) {
-		t.Parallel()
-
 		logger := testutil.Logger(t)
 		ctx := testutil.Context(t, testutil.WaitMedium)
 		// Create a test server
@@ -265,8 +257,6 @@ func TestUseKeyring(t *testing.T) {
 	})
 
 	t.Run("DisableKeyringWithFlag", func(t *testing.T) {
-		t.Parallel()
-
 		logger := testutil.Logger(t)
 		ctx := testutil.Context(t, testutil.WaitMedium)
 		client := coderdtest.New(t, nil)