Tim Duesterhus c6b9ba80ae CI: Update to actions/checkout@v6
No functional change, but we should keep this current.

see 5f4ddb54b05ae0355b1f64c22263a6bc381410df
see 5c923f1869881156bf3a25c9659655ae10f7dbd0
see b81a7f428bc0ae32df485c4c15637230eb60f459
2026-04-13 09:34:07 +02:00
..