Disable Spotlight indexing for the macOS build checks

The Intel appbundle build fails at the very last step, every time rather than
intermittently: the bundle is assembled, _verify_bundle_linkage passes, the SBOM
is written, the disk image is created and populated, and then create-dmg cannot
unmount it.

    Unmounting disk image...
    hdiutil: detach: timeout for DiskArbitration expired
    hdiutil: detach: drive not detached

Two runs, identical failure, and the gap between the unmount starting and the
timeout is exactly 120 seconds, so something is waiting out a timeout rather
than racing. Spotlight indexing the freshly mounted volume is the usual cause,
holding a DiskArbitration reservation that the detach then sits behind, and
nothing on a build runner wants a Spotlight index anyway.

arm64 has never shown this, so the step is harmless there rather than needed.
If this doesn't settle it, the next thing to try is macos-26-intel, and after
that a retry around the detach, which would mean changing pkg/mac rather than
the workflow.

.github/workflows/check-macos-build.yml

@@ -62,6 +62,17 @@ jobs:
       - name: Install the build dependencies
         run: brew install postgresql@18 openssl@3 syft wget
 
+      # create-dmg mounts a disk image and unmounts it again, and on the Intel
+      # runners that unmount reliably fails: "hdiutil: detach: timeout for
+      # DiskArbitration expired", exactly 120 seconds after it starts, with the
+      # bundle otherwise complete. Spotlight indexing the freshly mounted
+      # volume is the usual culprit, since it holds a DiskArbitration
+      # reservation the detach then waits out. Nothing on a build runner wants
+      # a Spotlight index. Harmless on arm64, which has never shown the
+      # problem.
+      - name: Disable Spotlight indexing
+        run: sudo mdutil -a -i off || true
+
       - name: Check the appbundle build
         run: |
           PGADMIN_POSTGRES_DIR="$(brew --prefix postgresql@18)"