use latest rust for non-windows, and upgrade tokio to 3.18 which fix a mpsc channel bug

.github/workflows/flutter-build.yml

@@ -11,7 +11,8 @@ on:
         default: "nightly"
 
 env:
-  RUST_VERSION: "1.75" # https://github.com/rustdesk/rustdesk/discussions/7503
+  WIN_RUST_VERSION: "1.75" # https://github.com/rustdesk/rustdesk/discussions/7503
+  RUST_VERSION: "1.78"
   CARGO_NDK_VERSION: "3.1.2"
   LLVM_VERSION: "15.0.6"
   FLUTTER_VERSION: "3.19.6"
@@ -84,7 +85,7 @@ jobs:
       - name: Install Rust toolchain
         uses: dtolnay/rust-toolchain@v1
         with:
-          toolchain: ${{ env.RUST_VERSION }}
+          toolchain: ${{ env.WIN_RUST_VERSION }}
           targets: ${{ matrix.job.target }}
           components: "rustfmt"