CI: Lock REST Fixture to 1.10.1

[Fokko]

With the new Jetty upgrade in apache/iceberg#10837 we're running into the following:

Failing CI: https://github.com/apache/iceberg-python/actions/runs/24416422109/job/71326697962

Malformed request: {
"message":"Suspicious Path Character",
"url":"http://rest:8181/v1/namespaces/default%1Ftest_positional_mor_deletes_v2/tables/branch_without_5?snapshots=all",
"status":"400"
}

The namespace-seperator has been introduced afther the 1.10.x branch (#2826), so it isn't out in public, meaning the Spark integration tests are not respecting this config. This requires us to downgrade for now.

I think disallowing the default (%1F) separator is problematic, since it might break compatibility.

Rationale for this change

Are these changes tested?

Are there any user-facing changes?

[geruh]

Thanks for raising this Fokko!

Looks like in the upgrade Jetty 12 is rejecting %1f in URL path, and the spark container uses the latest iceberg release 1.10.1 that hard codes that character for multi level namespaces. Looks like provision was failing because the branch target reference like this DELETE FROM {identifier}.branch_without_5 gets read as a multi-levl ns before reaching spark catalog.

Pinning works but now maybe we should skip the test_rest_custom_namespace_separator since 1.10.1 doesn't advertise the separator in the config call anymore.

WDYT @Fokko?