Add nightly check (tari-project#99)

This PR adds a nightly check to CI; this may help catch issues for downstream use of the library.

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
         run: cargo install cargo-lints
       - name: Lints
         run: cargo lints clippy --all-targets --all-features
-  check:
+  check-stable:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
@@ -39,6 +39,15 @@ jobs:
         run: cargo check --all-targets --no-default-features
       - name: Check (all features)
         run: cargo check --all-targets --all-features
+  check-nightly:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - name: Check (no features)
+        run: cargo check --all-targets --no-default-features
+      - name: Check (all features)
+        run: cargo check --all-targets --all-features
   docs:
     runs-on: ubuntu-latest
     steps: