CI: Set up Rust compiler

Author: dnicolodi

.github/workflows/tests.yml

@@ -137,6 +137,9 @@ jobs:
         run: python -m pip install ${{ matrix.dependencies }}
         if: ${{ matrix.dependencies }}
 
+      - name: Set up Rust compiler
+        run: rustup override set nightly
+
       - name: Install
         run: python -m pip install . --group test