ci: fix requirements diff check crash [backport 2.1] (#7823)

Backport 0dba5d5 from #7815 to 2.1.

This change fixes a silent failure of `scripts/check-diff` that can
result in outdated riot lockfiles being committed to trunk. The failure
is caused by the use of the `-I` option to `git diff` on versions of git
too old to support that option, such as the version installed in the
testrunner container used in CI.

## Checklist

- [x] Change(s) are motivated and described in the PR description.
- [x] Testing strategy is described if automated tests are not included
in the PR.
- [x] Risk is outlined (performance impact, potential for breakage,
maintainability, etc).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed. If no release note is required, add label
`changelog/no-changelog`.
- [x] Documentation is included (in-code, generated user docs, [public
corp docs](https://github.com/DataDog/documentation/)).
- [x] Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist

- [x] Title is accurate.
- [x] No unnecessary changes are introduced.
- [x] Description motivates each change.
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes unless absolutely necessary.
- [x] Testing strategy adequately addresses listed risk(s).
- [x] Change is maintainable (easy to change, telemetry, documentation).
- [x] Release note makes sense to a user of the library.
- [x] Reviewer has explicitly acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment.
- [x] Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)
- [x] If this PR touches code that signs or publishes builds or
packages, or handles credentials of any kind, I've requested a review
from `@DataDog/security-design-and-guidance`.
- [x] This PR doesn't touch any of that.

Co-authored-by: Emmett Butler <[email protected]>

Author: github-actions[bot]

scripts/check-diff

@@ -2,10 +2,10 @@
 
 directory=${1:-"."}
 message=${2:-"Files were changed or added."}
-changed_files="$(git diff -I '^#' -- ${directory})"
+changed_files="$(git diff -G'^[^#]' -- ${directory})"
 new_files="$(git ls-files -o --exclude-standard -- ${directory})"
 
-if [[ "$(git diff -I '^#' --exit-code -- ${directory})" || -n $new_files ]]
+if [[ "$(git diff -G'^[^#]'  --exit-code -- ${directory})" || -n $new_files ]]
 then
     echo "${changed_files}"
     echo "${new_files}"