Update glib requirement from 0.18.5 to 0.21.5

[dependabot]

Updates the requirements on glib to permit the latest version.

Release notes

Sourced from glib's releases.

0.21.5

Biagio Festa:
      glib/bytes: relax start offset constraint for `from_bytes`
Bilal Elmoussaoui:

ci: Add rustfmt component where needed
Sebastian Dröge:

Update gir

Regenerate with latest gir

glib: Fix typo in docs

ci: Only run glib-macros tests on stable

gio: Remove pointless, empty build.rs

glib: Fix Regex::match API

glib: Add some missing debug assertions to the Regex API

gio: Fix GSettings test

Remove --cfg docsrs from the Cargo.tomls

Update docs.rs hacks in cairo-sys build.rs

Don't pass --cfg docsrs via RUSTFLAGS on the CI

Update Cargo.lock

glib: Clean up Regex tests

Update versions to 0.21.5

Commits

• 8b65406 Update versions to 0.21.5
• 018693c glib: Clean up Regex tests
• 2129928 Update Cargo.lock
• 2405029 Don't pass --cfg docsrs via RUSTFLAGS on the CI
• 23953aa Update docs.rs hacks in cairo-sys build.rs
• 80bcc3e Remove --cfg docsrs from the Cargo.tomls
• a2c801f gio: Fix GSettings test
• 8dae429 glib: Add some missing debug assertions to the Regex API
• 8ec6bd9 glib: Fix Regex::match API
• fb7da24 gio: Remove pointless, empty build.rs
• Additional commits viewable in compare view

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