ci/update-other: generate branch list from version-info

Uses a sparse-checkout to download only the `version-info.toml` file,
then uses the `yq-go` action to extract the "other" branches as a JSON
array.

.github/workflows/update-other.yml

@@ -15,17 +15,21 @@ jobs:
     runs-on: ubuntu-24.04-arm
     if: github.repository == 'nix-community/nixvim'
     outputs:
-      branches: ${{ steps.list-branches.outputs.branches }}
+      branches: ${{ steps.list-branches.outputs.result }}
     steps:
+      - name: Checkout version-info
+        uses: actions/checkout@v4
+        with:
+          sparse-checkout: version-info.toml
+          sparse-checkout-cone-mode: false
       - name: List stable branches
         id: list-branches
-        run: |
-          echo 'branches<<EOF
-          [
-            "nixos-25.05",
-            "nixos-24.11"
-          ]
-          EOF' >> "$GITHUB_OUTPUT"
+        uses: mikefarah/yq@master
+        with:
+          cmd: |
+            yq --no-colors --output-format=json \
+              '[ .versions[].branch | select(. != "main") ]' \
+              version-info.toml
   update:
     name: Trigger update on ${{ matrix.branch }}
     runs-on: ubuntu-24.04-arm