Bump pytest from 6.2.5 to 9.0.3 in /testing

Bumps [pytest](https://github.com/pytest-dev/pytest) from 6.2.5 to 9.0.3.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/main/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/6.2.5...9.0.3)

---
updated-dependencies:
- dependency-name: pytest
  dependency-version: 9.0.3
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

testing/requirements.txt

@@ -1,7 +1,7 @@
 # see also? ../cli/requirements.txt
 
 # for testing (only)
-pytest==6.2.5
+pytest==9.0.3
 pyserial
 ecdsa  # already required by ckcc-protocol
 python-secp256k1==0.2.0