update .gitignore (#1760)

make sure,
deltachat-ios.xcworkspace/xcshareddata/WorkspaceSettings.xcsettings
is ignored. not sure if that file becomes in use by recent Xcode,
however it is marked as being untracked after migrating to new M1 mac.

(updating that .gitignore from https://www.gitignore.io/api/xcode ,
the source that was used before, fixed it)

.gitignore

@@ -29,8 +29,10 @@ xcuserdata/
 *.xcodeproj/*
 !*.xcodeproj/project.pbxproj
 !*.xcodeproj/xcshareddata/
+!*.xcodeproj/project.xcworkspace/
 !*.xcworkspace/contents.xcworkspacedata
 /*.gcno
+**/xcshareddata/WorkspaceSettings.xcsettings
 
 .DS_Store