ci: downgrade pip to 24.0 for httpx [backport 2.7]

[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-2.7 Commit report: c48bc09 Test service: dd-trace-py

:white_check_mark: 0 Failed, 161573 Passed, 10481 Skipped, 9h 55m 44.09s Total duration (2h 32m 44.68s time saved)

[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-06-26 16:35:53

Comparing candidate commit c48bc0978ee133de931ce1b5670f221de646ca8e in PR branch backport-9639-to-2.7 with baseline commit ca89da9614f99e3ac82288fbf087fb8bd2298d1e in branch 2.7.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 201 metrics, 9 unstable metrics.