Bump coverage[toml] from 7.6.11 to 7.6.12 in /core

Bumps [coverage[toml]](https://github.com/nedbat/coveragepy) from 7.6.11 to 7.6.12.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.11...7.6.12)

---
updated-dependencies:
- dependency-name: coverage[toml]
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

core/pyproject.toml

@@ -60,7 +60,7 @@ classifiers = [
 # Extras used by developers *of* Toga are pinned to specific versions to
 # ensure environment consistency.
 dev = [
-    "coverage[toml] == 7.6.11",
+    "coverage[toml] == 7.6.12",
     "coverage-conditional-plugin == 0.9.0",
     "Pillow == 11.1.0",
     "pre-commit == 4.1.0",