pin nightly

rust-lang/rust#88679 (comment)

Author: trevyn

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, macos-11.0]
-        rust: [1.56, stable, beta, nightly]
+        rust: [1.56, stable, beta, nightly-2022-01-25]
 #              1.56 is minimum rust-version
     steps:
       - uses: actions/checkout@v2