ci: Run clippy on all OSs (#1547)

Have updated the CI config to run clippy on all OSs. This will catch 
any issues in OS specific codes. This might increase the amount of
annotations that are created in any of the common code but it should
be better than the alternative.

.github/workflows/workflow.yml

@@ -1,3 +1,4 @@
+---
 name: Main workflow
 on:
   push:
@@ -32,7 +33,10 @@ jobs:
   # Run the `clippy` linting tool
   clippy:
     name: Clippy [Linter]
-    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macOS-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
     steps:
       - name: Setup | Checkout
         uses: actions/checkout@v2