Skip deleted files when checking for e2e only spec files

What does this MR do and why?

Fixes https://gitlab.com/gitlab-org/quality/team-tasks/-/issues/1150

With this MR, if an MR changes only e2e tests, we were running 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. This MR fixes that issue.

Screenshots or screen recordings

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How to set up and validate locally

1. MR only changes e2e tests: PROJECT_TOKEN_FOR_CI_SCRIPTS_API_USAGE="super-secret-token" CI_API_V4_URL="https://www.gitlab.com//api/v4" CI_MERGE_REQUEST_PROJECT_PATH="gitlab-org/gitlab" CI_MERGE_REQUEST_IID="78034" tooling/bin/find_changes ~/temp/qa_changed_files.txt
2. MR deletes e2e test file: PROJECT_TOKEN_FOR_CI_SCRIPTS_API_USAGE="super-secret-token" CI_API_V4_URL="https://www.gitlab.com//api/v4" CI_MERGE_REQUEST_PROJECT_PATH="gitlab-org/gitlab" CI_MERGE_REQUEST_IID="77945" tooling/bin/find_changes ~/temp/qa_changed_files.txt
3. MR changes e2e specs and other files: PROJECT_TOKEN_FOR_CI_SCRIPTS_API_USAGE="super-secret-token" CI_API_V4_URL="https://www.gitlab.com//api/v4" CI_MERGE_REQUEST_PROJECT_PATH="gitlab-org/gitlab" CI_MERGE_REQUEST_IID="77666" tooling/bin/find_changes ~/temp/qa_changed_files.txt

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.