Update dependency gitreleasemanager.tool to v0.20.0

Author: renovate[bot]

.config/dotnet-tools.json

@@ -9,7 +9,7 @@
       ]
     },
     "gitreleasemanager.tool": {
-      "version": "0.18.0",
+      "version": "0.20.0",
       "commands": [
         "dotnet-gitreleasemanager"
       ]