[SPARK-45008][INFRA] Improve branch suggestion for backporting

[yaooqinn]

What changes were proposed in this pull request?

This PR automatically iterates to the next branch to be merged instead of using the latest all the time

Why are the changes needed?

anti-misoperation

Does this PR introduce any user-facing change?

no

How was this patch tested?

Was this patch authored or co-authored using generative AI tooling?

Locally tested

>>> def get_json(url):
...     try:
...         request = Request(url)
...         if GITHUB_OAUTH_KEY:
...             request.add_header("Authorization", "token %s" % GITHUB_OAUTH_KEY)
...         return json.load(urlopen(request))
...     except HTTPError as e:
...         if "X-RateLimit-Remaining" in e.headers and e.headers["X-RateLimit-Remaining"] == "0":
...             print(
...                 "Exceeded the GitHub API rate limit; see the instructions in "
...                 + "dev/merge_spark_pr.py to configure an OAuth token for making authenticated "
...                 + "GitHub requests."
...             )
...         else:
...             print("Unable to fetch URL, exiting: %s" % url)
...         sys.exit(-1)
...
>>> branches = get_json("%s/branches" % GITHUB_API_BASE)
>>>
>>> branch_names = list(filter(lambda x: x.startswith("branch-"), [x["name"] for x in branches]))
>>> branch_names = sorted(branch_names, reverse=True)
>>> branch_iter = iter(branch_names)
>>> print(next(branch_iter, branch_names[0]))
branch-3.5
>>> print(next(branch_iter, branch_names[0]))
branch-3.4
>>> print(next(branch_iter, branch_names[0]))
branch-3.3
>>> print(next(branch_iter, branch_names[0]))
branch-3.2
>>> print(next(branch_iter, branch_names[0]))
branch-3.1
>>> print(next(branch_iter, branch_names[0]))
branch-3.0
>>> print(next(branch_iter, branch_names[0]))
branch-2.4
>>> print(next(branch_iter, branch_names[0]))
branch-2.3
>>> print(next(branch_iter, branch_names[0]))
branch-2.2
>>> print(next(branch_iter, branch_names[0]))
branch-2.1
>>> print(next(branch_iter, branch_names[0]))
branch-2.0
>>> print(next(branch_iter, branch_names[0]))
branch-1.6
>>> print(next(branch_iter, branch_names[0]))
branch-1.5
>>> print(next(branch_iter, branch_names[0]))
branch-1.4
>>> print(next(branch_iter, branch_names[0]))
branch-1.3
>>> print(next(branch_iter, branch_names[0]))
branch-1.2
>>> print(next(branch_iter, branch_names[0]))
branch-1.1
>>> print(next(branch_iter, branch_names[0]))
branch-1.0-jdbc
>>> print(next(branch_iter, branch_names[0]))
branch-1.0
>>> print(next(branch_iter, branch_names[0]))
branch-0.9
>>> print(next(branch_iter, branch_names[0]))
branch-0.8
>>> print(next(branch_iter, branch_names[0]))
branch-0.7
>>> print(next(branch_iter, branch_names[0]))
branch-0.6
>>> print(next(branch_iter, branch_names[0]))
branch-0.5
>>> print(next(branch_iter, branch_names[0]))
branch-3.5
>>> quit()

[yaooqinn]

cc @dongjoon-hyun @HyukjinKwon @cloud-fan thanks

[dongjoon-hyun]

+1, LGTM.

[yaooqinn]

thank you @dongjoon-hyun