Pin CI skeptic job to Rust 1.76

Author: dtolnay

.github/workflows/ci.yml

@@ -16,7 +16,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable]
+        # skeptic doesn't work since 1.77: bhttps://github.com/budziq/rust-skeptic/issues/141
+        rust: [1.76.0]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v4