[xharness] Do not trace the reflection exceptions used for the BCL. (#7634)

tests/Makefile

@@ -370,7 +370,7 @@ wrench-xtro:
 	@echo Not here anymore
 
 jenkins: xharness/xharness.exe
-	$(Q) $(SYSTEM_MONO) --trace=E:all --debug $(CURDIR)/$< $(XHARNESS_VERBOSITY) --jenkins --autoconf --rootdir $(CURDIR) --sdkroot $(XCODE_DEVELOPER_ROOT) --markdown-summary=$(abspath $(CURDIR))/TestSummary.md
+	$(Q) $(SYSTEM_MONO) --trace=E:all,-E:System.Reflection.ReflectionTypeLoadException --debug $(CURDIR)/$< $(XHARNESS_VERBOSITY) --jenkins --autoconf --rootdir $(CURDIR) --sdkroot $(XCODE_DEVELOPER_ROOT) --markdown-summary=$(abspath $(CURDIR))/TestSummary.md
 
 # This will launch xharness' interactive test runner in the system's default browser
 runner: xharness/xharness.exe