dev: improve runner to run dir with go.mod

[ldez]

Related to #3093 and #2969

Currently, we don't have any linter that required this approach, so I cannot add a test.

The test will look like that:

func TestSourcesFromTestdataSubDir(t *testing.T) {
	subDirs := []string{
		"logrlint",
		"ginkgolinter",
	}

	for _, dir := range subDirs {
		t.Run(dir, func(t *testing.T) {
			testSourcesFromDir(t, filepath.Join(testdataDir, dir))
		})
	}
}

[bombsimon]

🎉