Update continuous.yml

Author: zfergus

.github/workflows/continuous.yml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
+        os: [ubuntu-22.04, macos-latest, windows-latest]
         config: [Debug, Release]
         include:
           - os: macos-latest