fix uninitialized hash member in tests

Author: ludviggunne

lib/suppressions.h

@@ -52,7 +52,7 @@ class CPPCHECKLIB SuppressionList {
     };
 
     struct CPPCHECKLIB ErrorMessage {
-        std::size_t hash;
+        std::size_t hash{};
         std::string errorId;
         void setFileName(std::string s);
         const std::string &getFileName() const {