ci: Port from YAML anchors to GitLab extends

See https://docs.gitlab.com/ee/ci/yaml/yaml_optimization.html#use-extends-to-reuse-configuration-sections

Since we’re already using `extends` in other places in the configuration
file, it seems simpler to use it everywhere.

This should introduce no functional changes.

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>

.gitlab-ci.yml

@@ -235,7 +235,7 @@ valgrind:
       - "_build/glib/glibconfig.h"
       - "_build/meson-logs"
 
-.cross-template: &cross-template
+.cross-template:
   extends: .build
   stage: build
   needs: []
@@ -246,7 +246,7 @@ valgrind:
       - "_build/meson-logs"
 
 cross-android_api21_arm64:
-  <<: *cross-template
+  extends: .cross-template
   image: $ANDROID_IMAGE
   script:
     # FIXME: add --werror
@@ -256,7 +256,7 @@ cross-android_api21_arm64:
     - ninja -C _build
 
 cross-android_api28_arm64:
-  <<: *cross-template
+  extends: .cross-template
   image: $ANDROID_IMAGE
   script:
     # FIXME: add --werror
@@ -264,7 +264,7 @@ cross-android_api28_arm64:
     - ninja -C _build
 
 cross-mingw64:
-  <<: *cross-template
+  extends: .cross-template
   image: $MINGW_IMAGE
   script:
     # FIXME: Add --werror