chore: exclude errcheck linter from test files

Test files often ignore error returns for brevity and clarity,
especially for cleanup operations that don't affect test outcomes.

.golangci.yml

@@ -86,6 +86,7 @@ issues:
         - gochecknoglobals
         - mnd
         - unparam
+        - errcheck
 
     # Allow long lines in generated code or test data
     - path: ".*_gen\\.go"