build(deps): bump datadog from 0.38.0 to 0.39.0 in /backend

Bumps [datadog](https://github.com/DataDog/datadogpy) from 0.38.0 to 0.39.0.
- [Release notes](https://github.com/DataDog/datadogpy/releases)
- [Changelog](https://github.com/DataDog/datadogpy/blob/master/CHANGELOG.md)
- [Commits](DataDog/datadogpy@v0.38.0...v0.39.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/requirements.txt

@@ -1,6 +1,6 @@
 -e ../tools #egg=code-coverage-tools
 connexion==2.7.0
-datadog==0.38.0
+datadog==0.39.0
 fakeredis==1.4.3
 Flask==1.1.2
 Flask-Cors==3.0.8