Suppress ODR violation Cppcheck check for tests

Cppcheck treats the whole codebase as if it was to be compiled into a
single object and in tests we have some helper classes with the same
name in multiple executables.

.github/workflows/nightly.yml

@@ -78,6 +78,7 @@ jobs:
           cppcheck --quiet --language=c++ --force --inline-suppr
           --enable=warning,performance,portability,information
           --disable=missingInclude  --check-level=exhaustive
+          --suppress="ctuOneDefinitionRuleViolation:tests/*"
           -i build --library=std.cfg --error-exitcode=42 .
 
           if($LASTEXITCODE -eq 42) {