fix(build.yml): setup swift before running

Author: younke

.github/workflows/build.yml

@@ -16,6 +16,11 @@ jobs:
           - ubuntu-22.04
     runs-on: ${{ matrix.os }}
     steps:
+      - name: Install Swift (Ubuntu only)
+        if: runner.os == 'Linux'
+        uses: swift-actions/setup-swift@v2
+        with:
+          swift-version: "5.10"
       - name: asdf_plugin_test
         uses: asdf-vm/actions/plugin-test@v3
         with: