Update codecov.yml

Author: reiase

.github/workflows/codecov.yml

@@ -14,6 +14,13 @@ jobs:
     - uses: actions/setup-python@v2
       with:
         python-version: '3.9'
+    - name: Install Rust toolchain
+      uses: dtolnay/rust-toolchain@master
+      with:
+        toolchain: ${{ inputs.rust }}
+        targets: ${{ inputs.rust-target }}
+        # needed to correctly format errors, see #1865
+        components: rust-src
     - name: Install requirements
       run: |
         pip install pytest pytest-cov && pip install -e .