Add 5.7 toolchain matrix (#210)

* Add 5.7 toolchain matrix

* Reduce 5.5 toolchain matrix entries

* Use stable version

Author: kateinoigakukun

.github/workflows/test.yml

@@ -18,10 +18,11 @@ jobs:
           # Ensure that test succeeds with all toolchains and wasi backend combinations
           - { os: ubuntu-20.04, toolchain: wasm-5.5.0-RELEASE, wasi-backend: Node }
           - { os: ubuntu-20.04, toolchain: wasm-5.6.0-RELEASE, wasi-backend: Node }
-          - { os: ubuntu-20.04, toolchain: wasm-5.5.0-RELEASE, wasi-backend: Wasmer }
+          - { os: ubuntu-20.04, toolchain: wasm-5.7.1-RELEASE, wasi-backend: Node }
           - { os: ubuntu-20.04, toolchain: wasm-5.6.0-RELEASE, wasi-backend: Wasmer }
-          - { os: ubuntu-20.04, toolchain: wasm-5.5.0-RELEASE, wasi-backend: MicroWASI }
+          - { os: ubuntu-20.04, toolchain: wasm-5.7.1-RELEASE, wasi-backend: Wasmer }
           - { os: ubuntu-20.04, toolchain: wasm-5.6.0-RELEASE, wasi-backend: MicroWASI }
+          - { os: ubuntu-20.04, toolchain: wasm-5.7.1-RELEASE, wasi-backend: MicroWASI }
 
     runs-on: ${{ matrix.entry.os }}
     steps: