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

[sebastianbergmann]

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.