Merge rust-bitcoin/rust-secp256k1#603: Add toolchain matrix to WASM job

77808b7d83 WIP: Add toolchain matrix to job (Tobin C. Harding)

Pull request description:

  Recently I changed CI to use the dtolnay runner and in doing so introduced a regression (knowingly) whereby we only ran the WASM tests with the stable toolchain.

  Run the WASM tests with multiple toolchains
  - stable
  - beta
  - 1.48.0
  - nightly

ACKs for top commit:
  apoelstra:
    ACK 77808b7d83

Tree-SHA512: c55fc31977082ad8332a7ae05267ca464294227a6542c251ea9ae367b6935e41a3ae27e8505c88ba69a85eca4a8600d46fed189be5033f7a7b85093038cf8590

.github/workflows/rust.yml

@@ -105,13 +105,16 @@ jobs:
   WASM:
     name: WASM
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        toolchain: [stable, beta, nightly, 1.48.0]
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v3
       - name: Install clang
         run: sudo apt-get install -y clang
       - name: Checkout Toolchain
-        uses: dtolnay/rust-toolchain@stable
+        uses: dtolnay/rust-toolchain@${{ matrix.toolchain }}
       - name: Running WASM tests
         env:
           DO_WASM: true