add various rust toolchains (#16)

let's get crazy

Author: joshuadavidthomas

.github/workflows/test.yml

@@ -18,10 +18,20 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [macos-latest, ubuntu-latest, windows-latest]
+        os:
+          - macos-latest
+          - ubuntu-latest
+          - windows-latest
+        toolchain:
+          - stable
+          - beta
+          - nightly
     steps:
       - uses: actions/checkout@v4
 
+      - name: Install Rust toolchain
+        run: rustup update ${{ matrix.toolchain }} && rustup default ${{ matrix.toolchain }}
+
       - name: Build
         run: cargo build --verbose