Bump mdl from 0.11.0 to 0.12.0

Note we need to update the indentation of nested unordered list due to a
change in MDL [1].

Bumps [mdl](https://github.com/mivok/markdownlint) from 0.11.0 to 0.12.0.
- [Changelog](https://github.com/markdownlint/markdownlint/blob/main/CHANGELOG.md)
- [Commits](https://github.com/mivok/markdownlint/compare/v0.11.0...v0.12.0)

---
updated-dependencies:
- dependency-name: mdl
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

[1] https://github.com/markdownlint/markdownlint/commit/67f8312aae

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

CONTRIBUTING.md

@@ -10,9 +10,9 @@ The prefered way to report any bug is [opening an issue in the project's repo](h
 
 * Try to use a descriptive and to-the-point title
 * It's a good idea to include some of these sections:
-  * Steps to reproduce the bug
-  * Expected behaviour/response
-  * Actual response
+   * Steps to reproduce the bug
+   * Expected behaviour/response
+   * Actual response
 * Sometimes it is also helpful if you mention your operating system, browser version and installed plugins.
 
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