Fix: Do not require t.Parallel if the function uses t.Setenv

[SimoTod]

This pull request updates the linter so it does not report an error when t.SetEnv is used.

For example

func TestSomething(t *testing.T) {
	t.Setenv("foo", "bar")

	t.Run("Test 1", func(t *testing.T) {
		t.Parallel()

		// actual test
	})

	t.Run("test 2", func(t *testing.T) {		                
		// actual test
	})
}

TestSomething cannot be run in parallel as it sets an env variable. However, once or more children could still be allowed to run in parallel. When combined to other linters like paralleltest, this conflicts and forces developers to add nolint comments to their tests.

Fixes #25