DOC: Enforce Numpy Docstring Validation for pandas.Series.backfill (#58526)

DOC: remove  -i pandas.Series.backfill PR01,SA01

Author: tuhinsharma121

ci/code_checks.sh

@@ -167,7 +167,6 @@ if [[ -z "$CHECK" || "$CHECK" == "docstrings" ]]; then
         -i "pandas.Series SA01" \
         -i "pandas.Series.__iter__ RT03,SA01" \
         -i "pandas.Series.add PR07" \
-        -i "pandas.Series.backfill PR01,SA01" \
         -i "pandas.Series.case_when RT03" \
         -i "pandas.Series.cat PR07,SA01" \
         -i "pandas.Series.cat.add_categories PR01,PR02" \