ci(ci_visibility): increase parallelism for pytest suite [backport 2.5] (#8173)

Backport 8bb3dd8 from #8168 to 2.5.

The `pytest` tests added in #7833 increased the runtime for the pytest
CircleCI suite.

This adds more parallelism to get the suite to execute faster.


https://app.circleci.com/pipelines/github/DataDog/dd-trace-py/54135/workflows/7e4c17d1-e66c-466d-913b-06b70ddb4415/jobs/3447481
shows 4x parallelism , and the job completing in ~10 minutes which is
bringing it back to a more reasonable timeframe.

## 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: Romain Komorn <[email protected]>

Author: github-actions[bot]

.circleci/config.templ.yml

@@ -916,6 +916,7 @@ jobs:
 
   pytest:
     <<: *machine_executor
+    parallelism: 4
     steps:
       - run_test:
           pattern: 'pytest'