Update CI workflow

Remove 18.04 since it is no longer supported by GitHub actions.
Add 22.04.

Signed-off-by: Jacob Perron <jacobmperron@gmail.com>

Author: jacobperron

.github/workflows/ci.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-18.04, ubuntu-20.04]
+        os: [ubuntu-20.04, ubuntu-22.04]
 
     steps:
     - name: Install dependencies