fix(osx): set BUNDLE_CAN_DOWNGRADE

Enables atomic replacement of the outer @APPLICATION_NAME@.app
payload during install/upgrade instead of PackageKit's default
file by file diff.

Without this, installing a rebranded client over an existing
install like a legacy client receipt being upgraded
via APPLICATION_REV_DOMAIN_INSTALLER can leave stale files from
the previous bundle mixed with the new payload, producing an
invalid code signature ("a sealed resource is missing or
invalid") that fails Gatekeeper/launchd validation on next boot.

Signed-off-by: Camila Ayres <camila.ayres@nextcloud.com>

Author: camilasan

admin/osx/macosx.pkgproj.cmake

@@ -17,6 +17,8 @@
 							<key>CHILDREN</key>
 							<array>
 								<dict>
+									<key>BUNDLE_CAN_DOWNGRADE</key>
+									<true/>
 									<key>CHILDREN</key>
 									<array/>
 									<key>GID</key>