Avoid Pygments 2.19.0 to fix Sphinx docs build

```
/home/runner/work/supervisor/supervisor/docs/configuration.rst:1145:Could not lex literal_block '[program:cat]\ncommand=/bin/cat\nprocess_name=%(program_name)s\nnumprocs=1\ndirectory=/tmp\numask=022\npriority=999\nautostart=true\nautorestart=unexpected\nstartsecs=10\nstartretries=3\nexitcodes=0\nstopsignal=TERM\nstopwaitsecs=10\nstopasgroup=false\nkillasgroup=false\nuser=chrism\nredirect_stderr=false\nstdout_logfile=/a/path\nstdout_logfile_maxbytes=1MB\nstdout_logfile_backups=10\nstdout_capture_maxbytes=1MB\nstdout_events_enabled=false\nstderr_logfile=/a/path\nstderr_logfile_maxbytes=1MB\nstderr_logfile_backups=10\nstderr_capture_maxbytes=1MB\nstderr_events_enabled=false\nenvironment=A="1",B="2"\nserverurl=AUTO' as "ini". Highlighting skipped.
```

tox.ini

@@ -38,6 +38,7 @@ deps =
 
 [testenv:docs]
 deps =
+    pygments >= 2.19.1  # Sphinx build fails on 2.19.0 when highlighting ini block
     Sphinx
     readme
     setuptools >= 18.5