ignore rider temp files (#9987)

Author: SimonCropp

.gitignore

@@ -190,3 +190,6 @@ artifacts/
 src/NuGetGallery/Content/gallery/css/bootstrap-theme.css
 src/NuGetGallery/Content/gallery/css/bootstrap.css
 src/NuGetGallery/Scripts/gallery/bootstrap.js
+
+#rider
+.idea/