Fix "Scala 2 syntax with -Xsource:3" warnings

[fthomas]

Since #3532 IntelliJ produced "Scala 2 syntax with -Xsource:3" warnings. This fixes them.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.78%. Comparing base (c75d82f) to head (238a79d).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3533   +/-   ##
=======================================
  Coverage   89.78%   89.78%           
=======================================
  Files         171      171           
  Lines        4983     4984    +1     
  Branches      504      484   -20     
=======================================
+ Hits         4474     4475    +1     
  Misses        509      509           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mzuehlke]

Did you fix the manually ?
Can we define some scalafmt or scalafix rules so the are not coming back ?
OR some compiler flags, as we didn't had any warnings before (as far as I know)
Neither under Scala 2.13 nor Scala 3

[exoego]

LGTM

[fthomas]

Can we define some scalafmt or scalafix rules so the are not coming back ?

238a79d should do that.