Constify various autoregistry globals to avoid clang-tidy complaints

Closes #2582

src/catch2/internal/catch_main.cpp

@@ -14,7 +14,7 @@
 namespace Catch {
     CATCH_INTERNAL_START_WARNINGS_SUPPRESSION
     CATCH_INTERNAL_SUPPRESS_GLOBALS_WARNINGS
-    static LeakDetector leakDetector;
+    static const LeakDetector leakDetector;
     CATCH_INTERNAL_STOP_WARNINGS_SUPPRESSION
 }