update msrv

Author: connortsui20

.github/workflows/check.yml

@@ -116,7 +116,7 @@ jobs:
     # https://docs.github.com/en/actions/learn-github-actions/contexts#context-availability
     strategy:
       matrix:
-        msrv: ["1.56.1"] # 2021 edition requires 1.56
+        msrv: ["1.78.0"] # `Cargo.lock` version 4
     name: ubuntu / ${{ matrix.msrv }}
     steps:
       - uses: actions/checkout@v4