[FYI] CI Infra issues (in both GitHub Action and Jenkins)

[Dongjoon Hyun]

Hi, All.

There are two issues currently.

1. Jenkins machines start to fail with the following recently.
    (master branch)

    Python versions prior to 3.6 are not supported.
    Build step 'Execute shell' marked build as failure

2. Lack of GitHub Action backend machines.

    There is a JIRA to ask us to reduce the usage.
    https://issues.apache.org/jira/browse/SPARK-34053
    "Please reduce GitHub Actions matrix or improve the build time"

Bests,
Dongjoon.