lint: consider to add helper marker for functions in test files

[cristaloleg]

before:

// code_test.go
func testHelper(t *testing.T, params ...interface{}) interface{} {
    ...
}

after:

// code_test.go
func testHelper(t *testing.T, params ...interface{}) interface{} {
    t.Helper()
    ...
}

This will exclude noisy(?) testHelper from a stacktrace.

[Antonboom]

Covered by https://golangci-lint.run/usage/linters/#thelper