overlay profiles: Temporarily mask intel-microcode update

It is just too large - takes too much space in /boot, which causes
update failures.

Author: krnowak

sdk_container/src/third_party/coreos-overlay/profiles/coreos/base/package.mask

@@ -20,3 +20,8 @@
 
 # Pulls in LLVM and clang.
 >=sys-block/thin-provisioning-tools-1.0.14
+
+# Too large to fit into our /boot partition - the size grew by 3MB. We
+mask a specific version in hope that the future update may be smaller,
+who knows.
+=sys-firmware/intel-microcode-20250512_p20250513