Use normal severity for Phan checks

[MorrisJobke]

Extracted from #8375

[codecov]

Codecov Report

Merging #9314 into master will decrease coverage by 45.18%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master   #9314       +/-   ##
============================================
- Coverage     51.93%   6.74%   -45.19%     
  Complexity    25388   25388               
============================================
  Files          1608    1608               
  Lines         95440   95440               
  Branches       1394    1394               
============================================
- Hits          49563    6437    -43126     
- Misses        45877   89003    +43126

Impacted Files	Coverage Δ	Complexity Δ
apps/comments/lib/JSSettingsHelper.php	0% <0%> (-100%)	2% <0%> (ø)
lib/private/Security/CSRF/CsrfToken.php	0% <0%> (-100%)	5% <0%> (ø)
apps/files/lib/Activity/Settings/FileChanged.php	0% <0%> (-100%)	8% <0%> (ø)
...curity/Exceptions/StrictCookieMissingException.php	0% <0%> (-100%)	1% <0%> (ø)
apps/user_ldap/lib/Mapping/UserMapping.php	0% <0%> (-100%)	1% <0%> (ø)
apps/user_ldap/lib/Migration/UUIDFixGroup.php	0% <0%> (-100%)	1% <0%> (ø)
apps/files/appinfo/app.php	0% <0%> (-100%)	0% <0%> (ø)
apps/encryption/lib/Users/Setup.php	0% <0%> (-100%)	6% <0%> (ø)
...yBuilder/FunctionBuilder/SqliteFunctionBuilder.php	0% <0%> (-100%)	1% <0%> (ø)
lib/private/Hooks/LegacyEmitter.php	0% <0%> (-100%)	1% <0%> (ø)
... and 866 more

[MorrisJobke]

Okay this causes ~1200 warnings -> let's do this later