Update CI Rust version

Author: chipshort

.circleci/config.yml

@@ -90,7 +90,7 @@ workflows:
           matrix:
             parameters:
               # Run with MSRV and some modern stable Rust
-              rust-version: ["1.74.0", "1.77.0"]
+              rust-version: ["1.74.0", "1.78.0"]
       - benchmarking:
           requires:
             - package_vm