allow the actions user to login via the jwt token

[bohde]

We have some actions that leverage the Gitea API that began receiving 401 errors, with a message that the user was not found. These actions use the ACTIONS_RUNTIME_TOKEN env var in the actions job to authenticate with the Gitea API. The format of this env var in actions jobs changed with /pull/28885 to be a JWT (with a corresponding update to act_runner) Since it was a JWT, the OAuth parsing logic attempted to parse it as an OAuth token, and would return user not found, instead of falling back to look up the running task and assigning it to the actions user.

This restores that functionality by parsing Actions JWTs first, and then attempting to parse Oauth JWTs. The code to parse potential old ACTION_RUNTIME_TOKEN was kept in case someone is running an older version of act_runner that doesn't support the Actions JWT.

[bohde]

Here's a minimal action workflow that previously worked before the linked PR, running on a server with setting.Service.RequireSignInView == true :

name: Check Server Version
on: [push]
jobs:
  check-server-version:
    runs-on: ubuntu-latest
    steps:
      - name: Output Server Version
        run: |
          curl -H "Authorization: token $ACTIONS_RUNTIME_TOKEN"  "$GITHUB_SERVER_URL/api/v1/version"

[wxiaoguang]

Overall LGTM except the naming nit.

[GiteaBot]

I was unable to create a backport for 1.22. @bohde, please send one manually. 🍵

go run ./contrib/backport 32527
...  // fix git conflicts if any
go run ./contrib/backport --continue