fix(celery): ensure error.message tag does not include stacktrace [backport 2.10]

[github-actions[bot]]

Backport 16f3f951addfad0ba3b65235e601a9c101f273c6 from #9585 to 2.10.

Motivation

User reported that the celery exception traceback was being included in the error.message span tag. The error was due to us using the whole exception class, which includes the traceback, to set as the error message, instead of just the exception message. Updated test to ensure just error message is returned.

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

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

Datadog Report

Branch report: backport-9585-to-2.10 Commit report: 70bbbb0 Test service: dd-trace-py

:white_check_mark: 0 Failed, 194 Passed, 82 Skipped, 22m 2.2s Total duration (51.24s time saved)

[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-06-19 08:27:41

Comparing candidate commit d8d0c2a85937ed41524197528905a1eb790526ee in PR branch backport-9585-to-2.10 with baseline commit 70b27a25aa12e4b5dc46a542f7d36c41dd332f73 in branch 2.10.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 184 metrics, 0 unstable metrics.