ci: Exclude GitHub templates from markdownlint

The rule violations boil down to:
- MD002 First header should be a top level header: This makes no sense /
        looks very awkward in issue or PR descriptions.
- MD022 Headers should be surrounded by blank lines: It feels overly
        verbose to separate the comments from the headers given that
        there is no actual content here. Also remember this has to fit
        into the GitHub comment box, i.e. vertical space shouldn't be
        wasted if possible.
- MD026 Trailing punctuation in header: I can remove the colons from the
        issue template headers, but I think they make sense in this case
- MD012 Multiple consecutive blank lines: I left the newlines, because
        the user would have to always add them anyways.

Ref: #121

Author: BurningEnlightenment

.pre-commit-config.yaml

@@ -49,6 +49,7 @@ repos:
   rev: v0.12.0
   hooks:
   - id: markdownlint
+    exclude: ^\.github/(ISSUE_TEMPLATE/.*|pull_request_template)\.md$
 - repo: https://github.com/Holzhaus/sourceheaders
   rev: v0.0.4
   hooks: