Enable sparse registry access using the stable configuration

Exclude versions 1.66 and 1.67, which don't support stable sparse registry.

.github/workflows/ci.yml

@@ -15,7 +15,10 @@ jobs:
       matrix:
         rust: [
           # Test with toolchain file override
-          "1.50",
+          "1.60",
+          # Test that the sparse registry check works.
+          # 1.66 and 1.67 don't support stable sparse registry.
+          "1.66",
           "nightly",
           "beta",
           "stable",
@@ -33,7 +36,7 @@ jobs:
           profile = "minimal"
           EOF
         shell: bash
-        if: matrix.rust == '1.50'
+        if: matrix.rust == '1.60'
 
       - uses: ./
         name: Run actions-rust-lang/setup-rust-toolchain ${{matrix.rust}}
@@ -48,3 +51,10 @@ jobs:
         run: echo '${{steps.toolchain.outputs.rustup-version}}'
       - run: rustc --version && cargo --version
         shell: bash
+
+      # Test with creating a small project
+      - run: cargo init . --bin --name CI
+      # Add tiny empty crate.
+      # This checks that registry access works.
+      - run: cargo add serde_as
+      - run: cargo check