Update dependency ruff to v0.15.21 (#371)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>
Co-authored-by: Joakim Sørensen <joasoe@proton.me>

Author: renovate[bot]

requirements.txt

@@ -1,4 +1,4 @@
 colorlog==6.10.1
 homeassistant==2026.3.2
 pip>=21.3.1
-ruff==0.15.7
+ruff==0.15.21