Specify toolchain in CI

Author: llGaetanll

.github/workflows/ci.yml

@@ -14,6 +14,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
+          toolchain: nightly-2025-06-23
           components: rustfmt
       - run: cargo fmt --check
 
@@ -23,4 +24,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: nightly-2025-06-23
       - run: cargo test