tools: add coverage to ignored files

This adds the coverage directory to the .gitignore file.

PR-URL: #28626
Reviewed-By: Anna Henningsen <[email protected]>
Reviewed-By: Masashi Hirano <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: Сковорода Никита Андреевич <[email protected]>
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Rich Trott <[email protected]>

.gitignore

@@ -105,6 +105,7 @@ _UpgradeReport_Files/
 # coverage related
 /gcovr
 /build
+/coverage
 
 # === Rules for XCode artifacts ===
 *.xcodeproj