Fix typos in the code base (#2206)

Note that only documentation and comments are impacted by this change.

src/catch2/internal/catch_enum_values_registry.cpp

@@ -21,7 +21,7 @@ namespace Catch {
             // Extracts the actual name part of an enum instance
             // In other words, it returns the Blue part of Bikeshed::Colour::Blue
             StringRef extractInstanceName(StringRef enumInstance) {
-                // Find last occurence of ":"
+                // Find last occurrence of ":"
                 size_t name_start = enumInstance.size();
                 while (name_start > 0 && enumInstance[name_start - 1] != ':') {
                     --name_start;