Require flit-core v3.11+ to ensure license metadata in the distribution

[sisp]

The distributions of Click v8.1.8 (and probably some earlier ones) don't include license metadata fields. To confirm this, download the distributions and check click-8.1.8/PKG-INFO in the source distribution and click-8.1.8.dist-info/METADATA in the wheel distribution. According to my research, flit-core v3.11+ is needed for writing license file metadata, which was published on 2025-02-19, while Click v8.1.8 was published on 2024-12-21. As a result,

click/pyproject.toml

Line 5 in 934813e

license = {file = "LICENSE.txt"}

is omitted from the core metadata of the distributions when built with flit-core prior to v3.11.

In the meantime, v8.2.0+ got released which include license metadata fields in the distributions – but only coincidentally because flit-core v3.11+ had been released and flit-core<4 was resolved to v3.11+ then. But given the current license-related project metadata, only flit-core v3.11+ produces distributions that include license metadata, which can be ensured with a lower bound on flit-core, added in this PR. Long story for a minor change. 😄

[davidism]

Please rebase and retarget this to stable.

[sisp]

Done.