Add testing against TypeScript 5.0 beta

Author: Methuselah96

.github/workflows/test.yaml

@@ -98,7 +98,7 @@ jobs:
       fail-fast: false
       matrix:
         node: ['16.x']
-        ts: ['4.2', '4.3', '4.4', '4.5', '4.6', '4.7', '4.8', '4.9']
+        ts: ['4.2', '4.3', '4.4', '4.5', '4.6', '4.7', '4.8', '4.9', '5.0.0-beta']
     steps:
       - name: Checkout repo
         uses: actions/checkout@v2