update CI to temporarily not test Zig master

Author: Techatrix

.github/workflows/ci.yaml

@@ -14,13 +14,11 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        zig-version: [master]
+        zig-version: ["0.13.0"]
         os: [ubuntu-latest, macos-latest, windows-latest]
         include:
           - zig-version: "0.12.1"
             os: ubuntu-latest
-          - zig-version: "0.13.0"
-            os: ubuntu-latest
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout