Bump prometheus-client from 0.20.0 to 0.21.0 (#286)

Bumps [prometheus-client](https://github.com/prometheus/client_python) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/prometheus/client_python/releases)
- [Commits](prometheus/client_python@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: prometheus-client
  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>

requirements.txt

@@ -292,9 +292,9 @@ paramiko==3.5.0 \
     --hash=sha256:1fedf06b085359051cd7d0d270cebe19e755a8a921cc2ddbfa647fb0cd7d68f9 \
     --hash=sha256:ad11e540da4f55cedda52931f1a3f812a8238a7af7f62a60de538cd80bb28124
     # via -r requirements.in
-prometheus-client==0.20.0 \
-    --hash=sha256:287629d00b147a32dcb2be0b9df905da599b2d82f80377083ec8463309a4bb89 \
-    --hash=sha256:cde524a85bce83ca359cc837f28b8c0db5cac7aa653a588fd7e84ba061c329e7
+prometheus-client==0.21.0 \
+    --hash=sha256:4fa6b4dd0ac16d58bb587c04b1caae65b8c5043e85f778f42f5f632f6af2e166 \
+    --hash=sha256:96c83c606b71ff2b0a433c98889d275f51ffec6c5e267de37c7a2b5c9aa9233e
     # via -r requirements.in
 proxmoxer==2.1.0 \
     --hash=sha256:59d69abc5742c6c1b1737ce2944599136f66cdbbb1d044cd4b7aad30100ddde6 \