ci: pin hashbrown for msrv job (#2488)

* ci: pin hashbrown for msrv job

* ci: specify hashbrown@0.15.2

.github/workflows/ci.yml

@@ -298,6 +298,7 @@ jobs:
           cargo update -p tokio --precise 1.29.1
           cargo update -p tokio-util --precise 0.7.11
           cargo update -p idna_adapter --precise 1.1.0
+          cargo update -p hashbrown@0.15.2 --precise 0.15.0
 
       - uses: Swatinem/rust-cache@v2