fix: remove some extra newlines in sarif report

[G-Rath]

This is a bit nicer semantically imo and it also means the report is slightly smaller which is good.

I've not bothered dealing with the trailing , when there are multiple IDs as it seems like that would be a lot more work relative to the other changes so I don't think it's worth it

[codecov-commenter]

Codecov Report

Merging #607 (0742c08) into main (32ad454) will not change coverage.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #607   +/-   ##
=======================================
  Coverage   80.61%   80.61%           
=======================================
  Files          78       78           
  Lines        5334     5334           
=======================================
  Hits         4300     4300           
  Misses        866      866           
  Partials      168      168           

Files	Coverage Δ
internal/output/sarif.go	90.42% <ø> (ø)