Build/Release: fix RAT command

[kevinjqliu]

Following up to #15174
I accidentally added an extra --, causing the rest of the args to be treated as folder names

Also added exclusion for all .venv dir which is created by uv from site/ and open-api/

[kevinjqliu]

This PRs "Run License Check" CI job, https://github.com/apache/iceberg/actions/runs/21537468669/job/62065863825?pr=15194
now runs with the correct output

Run dev/check-license
Attempting to fetch rat
INFO: Apache Creadur RAT 0.17 (Apache Software Foundation)
SLF4J(W): No SLF4J providers were found.
SLF4J(W): Defaulting to no-operation (NOP) logger implementation
SLF4J(W): See https://www.slf4j.org/codes.html#noProviders for further details.
Files with missing headers:
RAT checks passed.