Fix msrv-check: async-lock bumped its MSRV

See https://github.com/smol-rs/async-lock/blob/master/CHANGELOG.md#version-342

Signed-off-by: Uli Schlachter <psychon@znc.in>

Author: psychon

.github/workflows/CI.yml

@@ -185,6 +185,8 @@ jobs:
       run: cargo update --package async-io --precise 2.5.0
     - name: Pin last polling release supporting our msrv of Rust 1.68
       run: cargo update --package polling --precise 3.10.0
+    - name: Pin last async-lock release supporting our msrv of Rust 1.68
+      run: cargo update --package async-lock --precise 3.4.1
 
     # build
     - name: cargo check x11rb-protocol with all features