Always build dmg installer in CI

Given that building a dmg is fast, just always build it instead of only
doing so when doing a release. This allows a user to download fixes and
new features quickly to test it out locally. Note that the dmg will be
unsigned, however, and not officially blessed by the team. This is
essentially a nightly build for the project.

Add a sane upper limit to retention days for dev builds, just in case we
end up making a lot of artifacts this way (since we are doing this per
every commit to master now).

Also, remove the previous "--skip-jenkins" hack we passed to create-dmg.
It was necessary in previous runners due to permission issues but it
seems like new GitHub Actions images have relaxed on that so the script
runs without that flag now. This allows us to beautify the dmg image in
CI.

.github/workflows/ci-macvim.yaml

@@ -384,27 +384,35 @@ jobs:
           make ${MAKE_BUILD_ARGS} -C src/testdir clean
           make ${MAKE_BUILD_ARGS} -C src testgui
 
-      # Creates a DMG package of MacVim. Note that this doesn't create a GitHub release for us, because we would prefer to
-      # do it manually, for two reasons: 1) signing / notarization are currently done out of CI, 2) we want to manually
-      # format our release notes and add pictures to make them look nice.
       - name: Build MacVim dmg image
-        if: startsWith(github.ref, 'refs/tags/') && matrix.publish
+        if: matrix.publish && (startsWith(github.ref, 'refs/tags/') || github.ref == 'refs/heads/master')
         run: |
           # Use the --skip-jenkins flag to skip the prettify osascript calls which could fail due to permission issues in
           # CI environment.
           if ${{ matrix.legacy == true }}; then
-            make -C src macvim-dmg-legacy CREATEDMG_FLAGS=--skip-jenkins
+            make -C src macvim-dmg-legacy
           else
-            make -C src macvim-dmg CREATEDMG_FLAGS=--skip-jenkins
+            make -C src macvim-dmg
           fi
 
           if ${{ matrix.publish_postfix != '' }}; then
             mv src/MacVim/build/Release/MacVim.dmg src/MacVim/build/Release/MacVim${{ matrix.publish_postfix }}.dmg
           fi
 
+      # Upload the dmg installer only when making tagged release or making a dev build from a master branch.
+      # Note that this doesn't create a GitHub release for us, because we would prefer to do it manually, for two
+      # reasons: 1) signing / notarization are currently done out of CI, 2) we want to manually format our release notes
+      # and add pictures to make them look nice. 
       - name: Upload MacVim image
-        if: startsWith(github.ref, 'refs/tags/') && matrix.publish
+        if: matrix.publish && (startsWith(github.ref, 'refs/tags/') || github.ref == 'refs/heads/master')
         uses: actions/upload-artifact@v4
         with:
           name: MacVim${{ matrix.publish_postfix  }}.dmg
           path: src/MacVim/build/Release/MacVim${{ matrix.publish_postfix }}.dmg
+
+          # If doing a tagged release, use repository-specified number of retention days (usually 90 days) to make it
+          # easier to audit. (specify "0" to indicate using repository settings)
+          #
+          # Otherwise, we are just doing a dev build for potential testing, just use a maximum of 21 days as we don't
+          # tend to need these for long.
+          retention-days: ${{ startsWith(github.ref, 'refs/tags/') && 0 || (github.retention_days > 21 && 21 || 0) }}