Datasets: use HTTPS for uber_tlc download URL

[shaun0927]

Issue #, if available: none

Description of changes:

src/gluonts/dataset/repository/_uber_tlc.py still uses plaintext HTTP to fetch the Uber TLC dataset from raw.githubusercontent.com. GitHub has served Raw content over HTTPS for years, so the HTTP URL only exists as a 2019-era artifact. Keeping it as HTTP has two downsides:

1. On a compromised network an attacker can replace the downloaded .zip with an arbitrary payload. The same file is then passed to zipfile.ZipFile.extractall on line 48, so any hostile zip member name that contains .. can land files outside temp_dir_path.
2. Some corporate/egress proxies refuse plain HTTP to GitHub entirely, making get_dataset("uber_tlc_hourly") fail on installs where every other dataset loader succeeds (those already use HTTPS).

This PR flips the single literal to https://. No other change is needed — GitHub Raw accepts the same path under HTTPS, and urllib.request.urlretrieve follows the scheme as given.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Please tag this pr with at least one of these labels to make our release process faster: BREAKING, new feature, bug fix, other change, dev setup