chore(deps): bump pyinstaller from 6.20.0 to 6.21.0 in /requirements

Bumps [pyinstaller](https://github.com/pyinstaller/pyinstaller) from 6.20.0 to 6.21.0.
- [Release notes](https://github.com/pyinstaller/pyinstaller/releases)
- [Changelog](https://github.com/pyinstaller/pyinstaller/blob/develop/doc/CHANGES.rst)
- [Commits](pyinstaller/pyinstaller@v6.20.0...v6.21.0)

---
updated-dependencies:
- dependency-name: pyinstaller
  dependency-version: 6.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements/pyinstaller-build.txt

@@ -1,2 +1,2 @@
 setuptools==82.0.1
-pyinstaller==6.20.0
+pyinstaller==6.21.0