Bump maccore. (#14417)

New commits in xamarin/maccore:

* xamarin/maccore@8287d19786 [submission] Only be optionally quiet.
* xamarin/maccore@5fe27fdd36 [submission] Add makefile target to add all the certs.
* xamarin/maccore@98670dcf31 [submission] Write results as tests are executed.

Diff: 696db0a953..8287d19786

Co-authored-by: Manuel de la Pena <mandel@microsoft.com>

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 := 696db0a953d62adc90cfbeaf42ebd1c901e7276b
+NEEDED_MACCORE_VERSION := 8287d1978617996f5a0f1c83c9264cc582c957fe
 NEEDED_MACCORE_BRANCH := main
 
 MACCORE_DIRECTORY := maccore