Pending PR filter excludes PRs due to skipped iceberg CI checks

[andygrove]

Problem

The pending PR filter in the README badge uses status:success, which excludes PRs that have all checks passing but also have skipped iceberg matrix jobs.

The iceberg workflow (iceberg_spark_test.yml) defines matrix jobs that skip when the PR title doesn't contain [iceberg]. When skipped before matrix expansion, GitHub reports checks with unexpanded names like:

• iceberg-spark/${{ matrix.os }}/iceberg-${{ matrix.iceberg-version.full }}/...

These skipped checks cause GitHub to not report the overall commit status as "success", so PRs like #3358 don't appear in the pending PR list despite all real checks passing.

Possible fixes

1. Change the filter from status:success to -status:failure so PRs are included unless they have actually failing checks
2. Fix the workflow to not report skipped checks — e.g. add a gate job that always succeeds and configure branch protection to use that instead of the individual matrix jobs
3. Move the if condition to the workflow trigger level so no checks are reported at all for non-iceberg PRs

Option 2 is the most robust but requires changing branch protection settings.

[andygrove]

@comphead any ideas for improving this?