chore: auto opt in all PRs to backport to 2.21

[erikayasuda]

Quick GitHub workflow to always label PRs with backport 2.21 so backporting to the 2.21 branch is an opt OUT, not an opt IN. This should help prevent critical backports from being missed in the 2.21 branch.

It will only skip PRs that are already backports, but by depending on the PR title.

Tested with this PR.

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:

.github/workflows/add-2x-backport-tag.yml                               @DataDog/python-guild @DataDog/apm-core-python

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 232 ± 5 ms.

The average import time from base is: 234 ± 4 ms.

The import time difference between this PR and base is: -1.5 ± 0.2 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 1.914 ms (0.82%)

ddtrace.bootstrap.sitecustomize 1.269 ms (0.55%)

ddtrace.bootstrap.preload 1.269 ms (0.55%)

ddtrace.internal.products 1.269 ms (0.55%)

ddtrace.internal.remoteconfig.client 0.624 ms (0.27%)

ddtrace 0.645 ms (0.28%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-04-02 17:50:26

Comparing candidate commit 513efe9 in PR branch erikayasuda/auto-backport-2.21 with baseline commit 4c46271 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 498 metrics, 2 unstable metrics.