Fix bugzilla 24600 - DMD nightly builds are outdated (#16580)

The artifact names have been changed in
dlang/installer@a842215,
because version 4 of actions/upload-artifact needs unique names.
Also use version 4 of actions/download-artifact and use a pattern instead of a single name.

See also https://github.com/actions/upload-artifact/blob/main/docs/MIGRATION.md

.github/workflows/nightlies.yml

@@ -36,9 +36,10 @@ jobs:
       # Fetch all artifacts from the jobs defined above
       #
       - name: Download generated releases from the artifacts
-        uses: actions/download-artifact@v3
+        uses: actions/download-artifact@v4
         with:
-          name: dmd-release
+          pattern: dmd-release-*
+          merge-multiple: true
           path: ~/artifacts/
 
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