Fix matching of non-lowercase filename tags

The bug was caused by forgetting to lower-case the filename tag
for matching against test spec.

Fixes #2064

src/catch2/catch_test_case_info.cpp

@@ -190,6 +190,9 @@ namespace Catch {
         std::string combined("#");
         combined += extractFilenamePart(lineInfo.file);
         internalAppendTag(combined);
+        // TBD: Running this over all tags again is inefficient, but
+        //      simple enough. In practice, the overhead is small enough.
+        toLowerInPlace(backingLCaseTags);
     }
 
     std::string TestCaseInfo::tagsAsString() const {