ci: Add codeowners for test_apps categories

.gitlab/CODEOWNERS

@@ -173,4 +173,10 @@
 /tools/ldgen/                 @esp-idf-codeowners/build-config
 /tools/mass_mfg/              @esp-idf-codeowners/app-utilities
 
+## Note: owners here should be the same as the owners for the same example subdir, above
+/tools/test_apps/build_system/       @esp-idf-codeowners/build-config
+/tools/test_apps/protocols/          @esp-idf-codeowners/network @esp-idf-codeowners/app-utilities
+/tools/test_apps/security/           @esp-idf-codeowners/security
+/tools/test_apps/system/             @esp-idf-codeowners/system
+
 requirements.txt              @esp-idf-codeowners/tools