treewide: parallel tests

Most tests already had no global state, however parallel was never enabled. This change enables it for all applicable tests.

Signed-off-by: Ophestra <cat@gensokyo.uk>

container/stub/errors_test.go

@@ -9,7 +9,10 @@ import (
 )
 
 func TestUniqueError(t *testing.T) {
+	t.Parallel()
+
 	t.Run("format", func(t *testing.T) {
+		t.Parallel()
 		want := "unique error 2989 injected by the test suite"
 		if got := stub.UniqueError(0xbad).Error(); got != want {
 			t.Errorf("Error: %q, want %q", got, want)
@@ -17,13 +20,17 @@ func TestUniqueError(t *testing.T) {
 	})
 
 	t.Run("is", func(t *testing.T) {
+		t.Parallel()
+
 		t.Run("type", func(t *testing.T) {
+			t.Parallel()
 			if errors.Is(stub.UniqueError(0), syscall.ENOTRECOVERABLE) {
 				t.Error("Is: unexpected true")
 			}
 		})
 
 		t.Run("val", func(t *testing.T) {
+			t.Parallel()
 			if errors.Is(stub.UniqueError(0), stub.UniqueError(1)) {
 				t.Error("Is: unexpected true")
 			}