Upgrade @octokit/rest to 19.0.3

This upgrade contains changes to the API types which leads to several changes
around the code base handling the now more precise types.

Signed-off-by: Crevil <bjoern.soerensen@gmail.com>

plugins/git-release-manager/package.json

@@ -31,7 +31,7 @@
     "@material-ui/core": "^4.12.2",
     "@material-ui/icons": "^4.9.1",
     "@material-ui/lab": "4.0.0-alpha.57",
-    "@octokit/rest": "^18.5.3",
+    "@octokit/rest": "^19.0.3",
     "luxon": "^2.0.2",
     "qs": "^6.10.1",
     "react-router": "6.0.0-beta.0",