Auto merge of #46393 - kennytm:45861-step-2-3-make-tools-job-not-fail-fast, r=alexcri...

Auto merge of #46393 - kennytm:45861-step-2-3-make-tools-job-not-fail-fast, r=alexcrichton

[auto-toolstate][2+3/8] Move external tools tests into its own job with --no-fail-fast

This PR performs these  things:

1. The `aux` job now performs "cargotest" and "pretty" tests. The clippy/rustfmt/rls/miri tests are moved into its own job.
2. These tests are run with `--no-fail-fast`, so that we can get the maximum number of failures of all tools from a single CI run.
3. The test results are stored into a JSON file, ready to be uploaded in the future.

This is step 2 and 3/8 of automatic management of broken tools #45861.