Reduce appveyor builds

appveyor.yml

@@ -3,6 +3,9 @@ version: '{build}'
 clone_folder: c:\projects\open62541
 clone_depth: 20
 
+# Avoid building branch if it is part of a PR and built anyways
+skip_branch_with_pr: true
+
 environment:
     global:
         APPVEYOR_CACHE_ENTRY_ZIP_ARGS: -t7z -m0=lzma -mx=9