fix(clang-tidy): skip conversion when const method calls non-const member

Author: bobtista

scripts/clang-tidy-plugin/readability/UseThisInsteadOfSingletonCheck.cpp

@@ -144,6 +144,9 @@ void UseThisInsteadOfSingletonCheck::check(
     if (Method->isStatic()) {
       return;
     }
+    if (EnclosingMethod->isConst() && !Method->isConst()) {
+      return;
+    }
     Member = Method;
     MemberName = Method->getName();
     StartLoc = MemberCall->getBeginLoc();