fix(tools/gitlab): address review follow-up on pagination docstring, short pages, and issue template

[Kaap10]

Addresses the two non-blocking follow-up observations from maintainer review in PR #1369:

1. tools/gitlab/issue-template.md

• Moved the SPDX-License-Identifier header above the doctoc Table of Contents block to conform to standard ASF file layout across the repository.
• Reworded the closing sentence to clarify that it serves as a descriptive reference for Markdown constructs in raw JSON issue/MR payloads.

2. tools/gitlab/src/magpie_gitlab/client.py & tools/gitlab/tests/test_client.py

• Corrected the test_get_paged_json_with_limit_fewer_than_page docstring from stating that it "emits notice" to "emits no notice", matching the actual assertion (err == "").
• Refined the pagination loop in get_paged_json to continue fetching subsequent pages when explicit --limit is specified and a short page (<100 items) is encountered with X-Next-Page set.
• Removed unused math import.
• Added test_get_paged_json_short_page_continues_until_limit to verify multi-page collection across short pages.

All 61 unit tests, mypy static typing, and ruff checks pass cleanly.

[Kaap10]

Hi @potiuk, opening this quick follow-up PR to address the two smaller observations from #1369.
Ready for review whenever you get a chance!

[potiuk]

Thanks — both follow-ups from #1369 are closed: with an explicit --limit the loop now keeps paging through short pages until the limit or the last page, max_pages only caps unlimited fetches (where the notice's "use --limit" remedy actually works), and the new test covers it. The docstring, SPDX placement and closing sentence are fixed too.

I pushed one small fixup on top (7eabef3): the change had also dropped the *generated with [DocToc](…)* suffix from the TOC title that every other doc keeps, so I restored it. Merging.

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