chore(build): Add extra builder

Sometimes the ubuntu-latest builder misses things that are different on
older runners, so include an older runner just to be sure.

.github/workflows/build.yml

@@ -1,10 +1,7 @@
 name: Rust Build
-
-on: [ push,  pull_request ]
-
+on: [push, pull_request]
 env:
   CARGO_TERM_COLOR: always
-
 jobs:
   cargo-deny:
     runs-on: ubuntu-latest
@@ -20,11 +17,11 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
-
+        os: [ubuntu-latest, ubuntu-20.04, macos-latest, windows-latest]
     steps:
-    - uses: actions/checkout@v3
-    - name: Build
-      run: cargo build --verbose
-    - name: Run tests
-      run: cargo test --verbose
+      - uses: actions/checkout@v3
+      - name: Build
+        run: cargo build --verbose
+      - name: Run tests
+        run: cargo test --verbose
+