[SPARK-23174][BUILD][PYTHON][FOLLOWUP] Add pycodestyle*.py to .gitignore file.

[ueshin]

What changes were proposed in this pull request?

This is a follow-up pr of #20338 which changed the downloaded file name of the python code style checker but it's not contained in .gitignore file so the file remains as an untracked file for git after running the checker.
This pr adds the file name to .gitignore file.

How was this patch tested?

Tested manually.

[ueshin]

cc @rekhajoshm @HyukjinKwon

[HyukjinKwon]

LGTM

[dongjoon-hyun]

+1, LGTM, too. :)

[rekhajoshm]

👍 LGTM @ueshin

[SparkQA]

Test build #86797 has finished for PR 20432 at commit 3fb3d78.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[ueshin]

Jenkins, retest this please.

[SparkQA]

Test build #86803 has finished for PR 20432 at commit 3fb3d78.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

retest this please

[SparkQA]

Test build #86818 has finished for PR 20432 at commit 3fb3d78.

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

[HyukjinKwon]

Merged to master.