Bump maccore. (#15748)

New commits in xamarin/maccore:

* xamarin/maccore@9a347bd708 [certificates] Update la_dev_apple.p12, la_distr_apple.p12 and la_mac_installer_distr.p12
* xamarin/maccore@bcdd779e58 [devops] Install Mono too.
* xamarin/maccore@7690a80a2f [submission] Fix submission test makefile

Diff: 813beaf11a..9a347bd708

mk/xamarin.mk

@@ -7,7 +7,7 @@ MONO_BRANCH    := $(shell cd $(MONO_PATH) 2> /dev/null && git symbolic-ref --sho
 endif
 
 ifdef ENABLE_XAMARIN
-NEEDED_MACCORE_VERSION := 813beaf11a3f5b3320c4ad8d4732542bd8b1bd09
+NEEDED_MACCORE_VERSION := 9a347bd708eb0ef975cf52cefdb23cb3a83d2690
 NEEDED_MACCORE_BRANCH := main
 
 MACCORE_DIRECTORY := maccore