gitlab-ci: update macOS jobs to use Xcode 12.0

.gitlab/os-macos.yml

@@ -7,7 +7,7 @@
         GIT_CLONE_PATH: "$CI_BUILDS_DIR/cmake ci ext/$CI_CONCURRENT_ID"
         # TODO: Factor this out so that each job selects the Xcode version to
         # use so that different versions can be tested in a single pipeline.
-        DEVELOPER_DIR: "/Applications/Xcode-11.7.app/Contents/Developer"
+        DEVELOPER_DIR: "/Applications/Xcode-12.0.app/Contents/Developer"
         # Avoid conflicting with other projects running on the same machine.
         SCCACHE_SERVER_PORT: 4227
 
@@ -63,7 +63,7 @@
         - cmake # Since this is a bare runner, pin to a project.
         - macos
         - shell
-        - xcode-11.7
+        - xcode-12.0
         - nonconcurrent
 
 .macos_builder_tags_package:
@@ -71,7 +71,7 @@
         - cmake # Since this is a bare runner, pin to a project.
         - macos
         - shell
-        - xcode-11.7
+        - xcode-12.0
         - nonconcurrent
         - finder
 
@@ -80,7 +80,7 @@
         - cmake # Since this is a bare runner, pin to a project.
         - macos
         - shell
-        - xcode-11.7
+        - xcode-12.0
         - concurrent
 
 ## macOS-specific scripts