ci: pin pytest [backport 2.7] (#8592)

Backport 7cc41ab from #8588 to 2.7.

CI: pin Pytest due to deprecations in the latest release.

Addresses failures like:
https://github.com/DataDog/dd-trace-py/actions/runs/8142342485/job/22251729134?pr=8565#step:8:371

## 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] Risks are described (performance impact, potential for breakage,
maintainability)
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] [Library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
are followed or label `changelog/no-changelog` is set
- [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))
- [x] If this PR changes the public interface, I've notified
`@DataDog/apm-tees`.
- [x] If change 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`.

## Reviewer Checklist

- [x] Title is accurate
- [x] All changes are related to the pull request's stated goal
- [x] Description motivates each change
- [x] Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- [x] Testing strategy adequately addresses listed risks
- [x] Change is maintainable (easy to change, telemetry, documentation)
- [x] Release note makes sense to a user of the library
- [x] Author has 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)

Co-authored-by: Federico Mon <federico.mon@datadoghq.com>

.github/workflows/test_frameworks.yml

@@ -58,7 +58,7 @@ jobs:
         if: needs.needs-run.outputs.outcome == 'success'
       # Taken from install script inside of .github/workflows of test suite (https://github.com/bottlepy/bottle/blob/master/.github/workflows/run_tests.yml)
         run: |
-          pip install -U pip pytest
+          pip install -U pip pytest==8.0.2
           pip install mako jinja2
           for name in waitress "cherrypy<9" cheroot paste tornado twisted diesel meinheld\
             gunicorn eventlet flup bjoern gevent aiohttp-wsgi uvloop; do