ci: drop support for python 3.7

[emmettbutler]

3.7 reached the end of its life recently https://peps.python.org/pep-0537/ ddtrace builds started failing a few hours ago because the centos mirror no longer hosts images that support Py37, as indicated by this error https://github.com/DataDog/dd-trace-py/actions/runs/9746783908/job/26897961608?pr=9672

Checklist

• [ ] Change(s) are motivated and described in the PR description
• [ ] Testing strategy is described if automated tests are not included in the PR
• [ ] Risks are described (performance impact, potential for breakage, maintainability)
• [ ] Change is maintainable (easy to change, telemetry, documentation)
• [ ] Library release note guidelines are followed or label changelog/no-changelog is set
• [ ] Documentation is included (in-code, generated user docs, public corp docs)
• [ ] Backport labels are set (if applicable)
• [ ] If this PR changes the public interface, I've notified @DataDog/apm-tees.

Reviewer Checklist

• [ ] Title is accurate
• [ ] All changes are related to the pull request's stated goal
• [ ] Description motivates each change
• [ ] Avoids breaking API changes
• [ ] Testing strategy adequately addresses listed risks
• [ ] Change is maintainable (easy to change, telemetry, documentation)
• [ ] Release note makes sense to a user of the library
• [ ] Author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• [ ] Backport labels are set in a manner that is consistent with the release branch maintenance policy

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

Datadog Report

Branch report: emmett.butler/bye37 Commit report: 6d95868 Test service: dd-trace-py

:white_check_mark: 0 Failed, 98310 Passed, 49022 Skipped, 3h 23m 45.83s Total duration (4h 45m 56.84s time saved)

[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-07-02 14:24:45

Comparing candidate commit 6d95868bb2612295d75a14126321d5d8ba6b01a0 in PR branch emmett.butler/bye37 with baseline commit 0cde594ca43b44889a38a058d639655caf5f640c in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 165 metrics, 9 unstable metrics.

[erikayasuda]

Closing this PR for now until we start planning for the next major upgrade.