test_pgdata_import_smoke failing frequently on pg17

[jcsp]

#10414 switched on postgres 17 version of this test, but it is timing out ~20% of the time.

Both sharded and non-sharded variants are affected.

Example failures:

• https://neon-github-public-dev.s3.amazonaws.com/reports/pr-6560/13026466544/index.html#testresult/a18c4709b7271a5b/retries
• https://neon-github-public-dev.s3.amazonaws.com/reports/pr-6560/13026466544/index.html#testresult/d3266108d5f8f1bf/retries

test_runner/regress/test_import_pgdata.py:256: in test_pgdata_import_smoke
    validate_vanilla_equivalence(ro_endpoint)
test_runner/regress/test_import_pgdata.py:116: in validate_vanilla_equivalence
    assert ep.safe_psql_many(
test_runner/fixtures/neon_fixtures.py:302: in safe_psql_many
    cur.execute(query)
/home/nonroot/.pyenv/versions/3.11.10/lib/python3.11/encodings/utf_8.py:15: in decode
    def decode(input, errors='strict'):
E   Failed: Timeout >300.0s