chore: Remove push triggers for CI

[comphead]

Which issue does this PR close?

Closes #.

Rationale for this change

When new PR is created it might start duplicated CI checks like in #3470

What changes are included in this PR?

Remove duplicate CI runs by disabling push triggers on PR workflows

Problem

Currently, workflows with both push and pull_request triggers run twice:

1. Once when you push commits to a branch (push event)
2. Again when the PR is created/updated (pull_request event)

This causes:

• Doubled CI resource usage - Same tests run twice unnecessarily
• Confusing status checks - Multiple check runs for the same commit
• Longer queue times - Duplicate jobs compete for runner capacity
• Wasted developer time - Waiting for redundant test results

Solution

Comment out push triggers in PR-focused workflows, keeping only pull_request:

• ✅ pr_build_linux.yml
• ✅ pr_build_macos.yml
• ✅ iceberg_spark_test.yml
• ✅ spark_sql_test.yml
• ✅ pr_benchmark_check.yml
• ✅ miri.yml
• ✅ validate_workflows.yml

Why pull_request is sufficient

The pull_request trigger runs when:

• A PR is opened
• New commits are pushed to the PR branch
• The PR is synchronized/updated

This covers all the validation needed before merging. Direct pushes to feature branches don't need separate CI runs since they'll be tested when the PR is created/updated.

Manual override still available

All workflows retain workflow_dispatch for manual triggering when needed.

How are these changes tested?

[andygrove]

Does this mean that the tests will no longer run on the main branch?

[comphead]

my understanding it should run for PR from feature to main as push changes to feature branches also triggers sync event and eventually pull_request.

UPD: check the DF and CI checks triggered by pull_request not by push