Upgrade to 1.15.2 breaks drone integration

[MGChecker]

After upgrading 1.14.5 -> 1.15.2, the drone integration is broken. This might be related to #16176.

• Gitea version (or commit ref): 1.15.3
• Git version:
• Operating system: Debian 11
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
• Log gist:

drone logs:

2021-09-11T18:49:48.383935235Z > {"commit":"61a0ac7422808ad435c04cac2da10b4a78fd4b1f","error":"Forbidden","event":"push","level":"warning","msg":"trigger: cannot find yaml","ref":"refs/heads/master","repo":"","time":"2021-09-11T18:49:48Z"}

gitea webhook:

Headers

Cache-Control: no-cache, no-store, must-revalidate, private, max-age=0
Content-Length: 99
Content-Type: application/json
Date: Sat, 11 Sep 2021 19:59:28 GMT
Expires: Thu, 01 Jan 1970 00:00:00 UTC
Pragma: no-cache
Server: Apache/2.4.38 (Debian)
X-Accel-Expires: 0
X-Frame-Options: DENY
X-Xss-Protection: 1; mode=block

Body

{"message":"json: cannot unmarshal object into Go struct field issue.issue.labels of type string"}

[MGChecker]

Apparently, this was some OAuth issue which could be fixed by using another user. Weird though.