[BUILD] Fix lint-python.

[ueshin]

What changes were proposed in this pull request?

This pr fixes lint-python.

./python/pyspark/accumulators.py:231:9: E306 expected 1 blank line before a nested definition, found 0
./python/pyspark/accumulators.py:257:101: E501 line too long (107 > 100 characters)
./python/pyspark/accumulators.py:264:1: E302 expected 2 blank lines, found 1
./python/pyspark/accumulators.py:281:1: E302 expected 2 blank lines, found 1

How was this patch tested?

Executed lint-python manually.

[gatorsmile]

LGTM

[SparkQA]

Test build #94033 has finished for PR 21973 at commit e405a9a.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[ueshin]

Thanks! merging to master.