CPack: use a distinct checksum file for each generator

Different CPack generators could produce checksum files with the same
name which were overwritten by each other since only package name
without extensions was used for checksum file name generation.  This
patch adds package extension to checksum files to prevent collisions.

Fixes: #16840

Source/CPack/cmCPackGenerator.cxx

@@ -999,8 +999,7 @@ int cmCPackGenerator::DoPackage()
     /* Generate checksum file */
     if (crypto.get() != nullptr) {
       std::string hashFile(this->GetOption("CPACK_OUTPUT_FILE_PREFIX"));
-      hashFile +=
-        "/" + filename.substr(0, filename.rfind(this->GetOutputExtension()));
+      hashFile += "/" + filename;
       hashFile += "." + cmSystemTools::LowerCase(algo);
       cmsys::ofstream outF(hashFile.c_str());
       if (!outF) {