refactor: Enable more clang-tidy readability checks (#6595)

Co-authored-by: Sergey Kuznetsov <kuzzz99@gmail.com>

src/test/app/AmendmentTable_test.cpp

@@ -439,7 +439,7 @@ public:
 
     // Make a list of trusted validators.
     // Register the validators with AmendmentTable and return the list.
-    std::vector<std::pair<PublicKey, SecretKey>>
+    static std::vector<std::pair<PublicKey, SecretKey>>
     makeValidators(int num, std::unique_ptr<AmendmentTable> const& table)
     {
         std::vector<std::pair<PublicKey, SecretKey>> ret;
@@ -462,7 +462,7 @@ public:
     }
 
     // Execute a pretend consensus round for a flag ledger
-    void
+    static void
     doRound(
         Rules const& rules,
         AmendmentTable& table,