Updating windows build constraints

pkg/guid is not windows specific, as it can run on Linux.
Build constraints on guid_windows and guid_nonwindows are redundant with
file names, but added for consistency.

Added missing build constraints.

Added Ubuntu to test matrix, along with windows 2022.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

.github/workflows/ci.yml

@@ -5,7 +5,10 @@ on:
 
 jobs:
   test:
-    runs-on: 'windows-2019'
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [windows-2019, windows-2022, ubuntu-latest]
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-go@v2