ci(serverless): force reimport of modules during serverless test

[purple4reina]

Commit 12655ee removed the @pytest.mark.subprocess() from the serverless slow imports test. This effectively rendered the test useless as ddtrace and all required modules had already been imported in the parent process.

Adding the subprocess mark back will ensure that the sys modules are fresh. We must still go through and delete entries because @pytest.mark.subprocess() relies on multiprocessing, so it must be removed so as to ensure it can be reimported if needed.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, 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

[github-actions]

CODEOWNERS have been resolved as:

.gitlab/tests.yml                                                       @DataDog/python-guild @DataDog/apm-core-python
tests/internal/test_serverless.py                                       @DataDog/apm-core-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: rey.abolofia/fix-sls-test
Commit report: 111226c
Test service: dd-trace-py

✅ 0 Failed, 130 Passed, 1468 Skipped, 4m 38.31s Total duration (35m 39.08s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-22 21:46:12

Comparing candidate commit 111226c in PR branch rey.abolofia/fix-sls-test with baseline commit 2f52abb in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 394 metrics, 2 unstable metrics.