ci: bump Rust toolchain to 1.90.0

New zbus and zvariant releases require a newer Rust compiler.

Use Rust 1.90.0 in CI so dependency resolution can complete.

Signed-off-by: Tim Zhang <tim@hyper.sh>

.github/workflows/bvt.yaml

@@ -1,7 +1,7 @@
 name: BVT
 on: [pull_request]
 env:
-  RUST_VERSION: 1.85.1
+  RUST_VERSION: 1.90.0
 jobs:
   build:
     name: Build
@@ -35,4 +35,3 @@ jobs:
       - run: rustup install ${{ env.RUST_VERSION }} && rustup default ${{ env.RUST_VERSION }}
       - run: make test
 
-