The keyboard layout indicator icon was always drawn at scale 1 and then
stretched by GTK+ to fit HiDPI outputs, making it blurrier than the
surrounding panel text.

This change renders both the flag image and the text-based icon at the
monitor's actual device scale so GTK+ can downscale instead of upscale.

Keyboard layout indicator text could render with subpixel antialiasing
even though SUBPIXEL was already avoided, because cairo falls back to
the font's own fontconfig antialiasing mode whenever the requested mode
is DEFAULT. This produced green/magenta color fringing on light-colored
indicator text.

Fixes #71

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Replace Travis CI configuration with GitHub Actions workflows.
Add CI build workflow for Debian, Fedora, Ubuntu, and Archlinux.
Add release workflow for automated GitHub releases on tags.
Add dependabot configuration for GHA pin updates.
Remove obsolete .travis.yml.