Merge pull request RustPython#3727 from fanninpm/beta-clippy

Switch clippy to beta

Author: youknowone

.github/workflows/ci.yaml

@@ -220,7 +220,7 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
             profile: minimal
-            toolchain: nightly
+            toolchain: beta
             components: rustfmt, clippy
             override: true
       - name: run rustfmt