ci: add 1.31 to the test matrix

Author: bevzzz

.github/workflows/main.yaml

@@ -14,6 +14,7 @@ env:
   WEAVIATE_128: 1.28.11
   WEAVIATE_129: 1.29.1
   WEAVIATE_130: 1.30.1
+  WEAVIATE_131: 1.31.0
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}