Update main.yml

Run check job in Ubuntu.

.github/workflows/main.yml

@@ -31,7 +31,7 @@ concurrency:
 # A workflow run is made up of one or more jobs that can run sequentially or in parallel
 jobs:
   check:
-    runs-on: matlab
+    runs-on: ubuntu-latest
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:  
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it