chore: use nightly toolchain for fmt job

Author: luisschwab

.github/pull_request_template.md

@@ -20,7 +20,7 @@ of the PR were done in a specific way -->
 
 * [ ] I've signed all my commits
 * [ ] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
-* [ ] I ran `cargo fmt` and `cargo clippy` before committing
+* [ ] I ran `cargo +nightly fmt` and `cargo clippy` before committing
 
 #### New Features:
 

.github/workflows/cont_integration.yml

@@ -117,7 +117,7 @@ jobs:
       - name: Install Rust toolchain
         uses: actions-rs/toolchain@v1
         with:
-            toolchain: ${{ needs.prepare.outputs.rust_version }}
+            toolchain: nightly
             override: true
             profile: minimal
             components: rustfmt