Update continuous_integration.yml

.github/workflows/continuous_integration.yml

@@ -1,12 +1,12 @@
 # Workflow for continuous integration tests
 name: CI
-on: [push, pull_request]
+on: [push, pull_request, workflow_dispatch]
 
 jobs:
   # This workflow contains a single job called "test"
   test:
     # The type of runner that the job will run on
-    runs-on: ubuntu-18.04
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         fortran-compiler: [gfortran]