Bump workflow MSRV to 1.75

Author: gahag-cw

.github/workflows/main.yml

@@ -36,7 +36,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: 1.70.0
+          toolchain: 1.75.0
       - run: cargo test -p bb8
 
   lint: