--format=sarif still outputs summary with using mix credo diff

[mashton]

Environment

• Credo version (mix credo -v): 1.7.7
• Erlang/Elixir version (elixir -v): Erlang 24/Elixir 1.16.3
• Operating system: macos 14.6.1

What were you trying to do?

use SARIF format as output, write to a file, and upload to GHAS

Expected outcome

> mix credo diff --from-git-merge-base origin/main  --format=sarif
{
    "just": "sarif formatted JSON"
}

Actual outcome

> mix credo diff --from-git-merge-base origin/main  --format=sarif
{
   "not_just": "sarif formatted JSON"
}
Diffing 3 source files in working dir with main ...
Please report incorrect results: https://github.com/rrrene/credo/issues
Analysis took 0.03 seconds (0.03s to load, 0.00s running 55 checks on 3 files)
Changes between <hash> and working dir:

+  added no issues,
✔  fixed no issues, and
~  kept no issues.

I'm totally willing to try my hand at a PR. Let me know if this seems to be a bug.