gitlab-ci: unmount images in `after_script`

.gitlab/ci/umount-dmg.sh

+#!/bin/sh
+
+set -e
+
+if ! [ -d "build/__mount" ]; then
+    exit 0
+fi
+
+# Detach the mount point.
+if ! hdiutil detach -verbose "build/__mount"; then
+    echo "Failed to detach mounted image…forcing"
+    hdiutil detach -force -verbose "build/__mount"
+fi

.gitlab/os-macos.yml

@@ -109,6 +109,9 @@
         - ctest -V --output-on-failure -S .gitlab/ci/ctest_package.cmake
         - sccache --show-stats
 
+    after_script:
+        - .gitlab/ci/umount-dmg.sh
+
     cache:
         key: macos
         paths: