build(deps): Bump elastic-apm from 6.20.0 to 6.21.3 (#331)

Bumps [elastic-apm](https://github.com/elastic/apm-agent-python) from 6.20.0 to 6.21.3.
- [Release notes](https://github.com/elastic/apm-agent-python/releases)
- [Changelog](https://github.com/elastic/apm-agent-python/blob/main/CHANGELOG.asciidoc)
- [Commits](elastic/apm-agent-python@v6.20.0...v6.21.3)

---
updated-dependencies:
- dependency-name: elastic-apm
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -5,7 +5,7 @@ future==1.0.0
 certifi
 dj-database-url==2.1.0
 django-redis==5.4.0
-elastic-apm==6.20.0
+elastic-apm==6.21.3
 elasticsearch==8.12.1
 elasticsearch-dsl==8.12.0
 elastic-transport==8.12.0