[testing] overrides: pin rust-zincati-0.0.25-6.fc39

[coreosbot-releng]

Requested by @dustymabe via GitHub workflow (source).

[dustymabe]

[2023-11-09T02:23:56.369Z] ostree diff commit from: 694d31bf9cdf1d365f7870e73f5c4d17b71e37562204beddcb76f587ecb65ca3
[2023-11-09T02:23:56.369Z] ostree diff commit to:   66f015edda80ccf46669eb38a338086f3ecc4246978cc9ec27c1018fccad6aa8
[2023-11-09T02:23:56.369Z] Downgraded:
[2023-11-09T02:23:56.369Z]   zincati 0.0.26-2.fc39 -> 0.0.25-6.fc39
[2023-11-09T02:23:56.369Z] + grep -q Downgraded tmp/diff.txt
[2023-11-09T02:23:56.369Z] + echo 'Downgrade detected. This is likely unintentional. If not, you may safely ignore this error.'
[2023-11-09T02:23:56.369Z] Downgrade detected. This is likely unintentional. If not, you may safely ignore this error.

👍 - this is what we want!