ci: downgrade pip to 24.0 for httpx [backport 2.9]

[gnufede]

HTTPX 0.22.0 requirements.txt uses a notation not compatible with latest pip (24.1).

This PR downgrades pip to 24.0 before trying to install HTTPX requirements.

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 are followed or label changelog/no-changelog is set
• [x] Documentation is included (in-code, generated user docs, public corp docs)
• [x] Backport labels are set (if applicable)
• [x] If this PR changes the public interface, I've notified @DataDog/apm-tees.

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 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

(cherry picked from commit 03650f8b59624561d33b0d138503a6bd700e8518)

[datadog-dd-trace-py-rkomorn[bot]]

Datadog Report

Branch report: backport-9639-to-2.9 Commit report: e6c57b2 Test service: dd-trace-py

:x: 8 Failed (0 Known Flaky), 134171 Passed, 41101 Skipped, 8h 50m 8.2s Total duration (2h 32m 49.01s time saved)

:x: Failed Tests (8)

This report shows up to 5 failed tests.

• test_on_executor_custom_kwarg - test_executor_decorator.py - Details

<details>
<summary>Expand for error</summary>

```
assert 'tornado-web' == None
 +  where None = <Span(id=9608657368736493768,trace_id=136226222172072777141779479708881717007,parent_id=264126342217236623,name=tornado.executor.with)>.service
```
</details>

• test_on_executor_custom_kwarg - test_executor_decorator.py - Details

  Expand for error

  ``` assert 'tornado-web' == None + where None = .service ```

• test_on_executor_exception_handler - test_executor_decorator.py - Details

  Expand for error

  ``` assert 'tornado-web' == None + where None = .service ```

• test_on_executor_exception_handler - test_executor_decorator.py - Details

  Expand for error

  ``` assert 'tornado-web' == None + where None = .service ```

• test_on_executor_handler - test_executor_decorator.py - Details

  Expand for error

  ``` assert 'tornado-web' == None + where None = .service ```

[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-06-26 16:34:57

Comparing candidate commit e6c57b20de68c3d9c2708f71ff45e8ec2dfaa9a9 in PR branch backport-9639-to-2.9 with baseline commit 072486e6ceb3cb036bb307b3025ca3bfc559155d in branch 2.9.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 209 metrics, 9 unstable metrics.