CI: use another glob syntax for matching files on Appveyor

The previous globbing syntax was not matching files recursively in
directories, so try appending a /* to more closely match the examples at
https://www.appveyor.com/docs/how-to/filtering-commits/

appveyor.yml

@@ -360,11 +360,11 @@ branches:
 skip_commits:
   files:
     - '.azure-pipelines.yml'
-    - '.circleci/**'
+    - '.circleci/**/*'
     - '.cirrus.yml'
-    - '.github/**'
-    - 'packages/**'
-    - 'plan9/**'
+    - '.github/**/*'
+    - 'packages/**/*'
+    - 'plan9/**/*'
 
 artifacts:
   - path: '**/curl.exe'