Test with the latest 5.5 snapshot (#138)

Author: MaxDesiatov

.github/workflows/test.yml

@@ -12,6 +12,7 @@ jobs:
         toolchain:
           - wasm-5.3.1-RELEASE
           - wasm-5.4.0-RELEASE
+          - wasm-5.5-SNAPSHOT-2021-09-01-a
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout