Change Swift workflow to Ubuntu and simplify triggers (#31)

Updated the Swift workflow to run on Ubuntu instead of macOS and
simplified the trigger conditions.

*Issue #, if available:*

*Description of changes:*


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Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: sebsto

.github/workflows/swift.yml

@@ -0,0 +1,22 @@
+# Simple test to obtain a green badge when merging to main branch
+
+name: Swift Simple Check
+
+permissions:
+  contents: read
+
+on:  
+  push:
+    branches: [ "main" ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build
+      run: swift build -v
+    - name: Run tests
+      run: swift test -v