Fix CI

Was failing with:

> The system library `glib-2.0` required by crate `glib-sys` was not found.

Author: wmanley

.github/workflows/rust.yml

@@ -18,6 +18,8 @@ jobs:
     - uses: actions/checkout@v2
     - name: Build
       run: cargo build --verbose
+    - name: Install glib for testing
+      run: apt-get install -y libglib2.0-dev
     - name: Run tests
       run: cargo test --verbose
     - name: Check formatting