Don't attempt testing with old SwiftWasm versions

Author: MaxDesiatov

.github/workflows/test.yml

@@ -10,9 +10,7 @@ jobs:
       matrix:
         os: [macos-10.15, macos-11, ubuntu-18.04, ubuntu-20.04]
         toolchain:
-          - wasm-5.3.1-RELEASE
-          - wasm-5.4.0-RELEASE
-          - wasm-5.5-SNAPSHOT-2021-09-01-a
+          - wasm-5.5-SNAPSHOT-2021-09-26-a
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout