branch-4.1: [fix](regression) Enable expression pushdown for variant norms test

[eldenmoon]

Follow-up to #68140.

Problem

test_variant_subcolumn_index_norms failed

match_phrase not support execute_match

The VARIANT MATCH predicate was not guaranteed to be pushed into the inverted index because the suite did not explicitly enable common expression pushdown. It then fell back to execute_match, which does not support MATCH_PHRASE.

Fix

Explicitly enable enable_common_expr_pushdown, matching the existing test_bm25_score_variant setup on branch-4.1.

Validation

• Confirmed TeamCity build 1051635 failed at the first VARIANT MATCH_PHRASE query after table creation and insertion succeeded.
• git diff --check passed.
• Local regression execution is unavailable because the branch-4.1 BE build is blocked by the local thirdparty/toolchain environment; CI is required for runtime confirmation.

[hello-stephen]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[eldenmoon]

run buildall