Deprecate support for using comma-separated values with the `--group`, `--exclude-group`, `--covers`, `--uses`, and `--test-suffix` CLI options

The `--group`, `--exclude-group`, `--covers`, `--uses`, and `--test-suffix` CLI options support comma-separated values.

For instance, `--group foo,bar` can be used to run the tests from the `foo` and `bar` groups. After #5708, `--group foo --group bar` should be used instead.