fix msrv

.github/workflows/check.yml

@@ -104,7 +104,7 @@ jobs:
     # https://docs.github.com/en/actions/learn-github-actions/contexts#context-availability
     strategy:
       matrix:
-        msrv: ["1.78.0"] # For lock file version 4
+        msrv: ["1.81.0"] # Start with first version that supports error_in_core
     name: ubuntu / ${{ matrix.msrv }}
     steps:
       - uses: actions/checkout@v4