When an MR changes only e2e tests but the change is a "file delete", do not include that file in QA_TESTS

With this MR, if an MR changes only e2e tests, run only those e2e tests by setting those tests to QA_TESTS env variable. But if the test file is deleted, it should not be added to QA_TESTS.

See this MR for example: gitlab-org/gitlab!73833 (merged)