GHA: limit 'Deploy Doxygen documentation' to main repo only

that workflow was accidently triggered in fork repo, where
there's no github pages set

Signed-off-by: Ilia Shipitsin <chipitsine@gmail.com>
Acked-by: Frank Lichtenheld <frank@lichtenheld.com>
Message-Id: <20250811161323.1599-1-chipitsine@gmail.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg32598.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

Author: chipitsine

.github/workflows/doxygen.yml

@@ -9,6 +9,7 @@ concurrency:
 jobs:
   build:
     runs-on: ubuntu-24.04
+    if: ${{ github.repository_owner == 'openvpn' || github.event_name == 'workflow_dispatch' }}
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with: