Disable clippy CI due to clippy crash

Clippy crash: rust-lang/rust-clippy#7423

    thread 'rustc' panicked at '`LateContext::typeck_results` called outside of body', src/tools/clippy/clippy_lints/src/use_self.rs:213:20
    note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

    error: internal compiler error: unexpected panic

    note: the compiler unexpectedly panicked. this is a bug.

    query stack during panic:
    #0 [analysis] running analysis passes on this crate
    end of query stack

Author: dtolnay

.github/workflows/ci.yml

@@ -96,7 +96,8 @@ jobs:
   clippy:
     name: Clippy
     runs-on: ubuntu-latest
-    if: github.event_name != 'pull_request'
+    #if: github.event_name != 'pull_request'
+    if: false  # Clippy crash: https://github.com/rust-lang/rust-clippy/issues/7423
     steps:
       - uses: actions/checkout@v2
       - uses: dtolnay/rust-toolchain@clippy