Make @githubpr sticky (#7342)

Author: alexr00

package.json

@@ -81,7 +81,8 @@
 				"name": "githubpr",
 				"fullName": "GitHub Pull Requests",
 				"description": "Chat participant for GitHub Pull Requests extension",
-				"when": "config.githubPullRequests.experimental.chat"
+				"when": "config.githubPullRequests.experimental.chat",
+				"isSticky": true
 			}
 		],
 		"configuration": {