fix msrv version in action

yaml is a pain

Signed-off-by: Robin Appelman <robin@icewind.nl>

.github/workflows/rust.yml

@@ -110,7 +110,7 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: 1.60
+          toolchain: "1.60"
           override: true
           target: x86_64-unknown-linux-musl
       - uses: Swatinem/rust-cache@v2.2.0