Disable markdownlint MD051 for attr_list anchors

The docs use python-markdown attr_list heading anchors like '{ #fr1 }' that
markdownlint's MD051 cannot resolve, producing false positives on valid
same-page requirement links. Test-DocumentationLink.ps1 is the authoritative
fragment validator and already recognises these anchors.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug

.github/linters/.markdown-lint.yml

@@ -21,6 +21,7 @@ MD029: false                  # Ordered list item prefix
 MD033: false                  # Allow inline HTML
 MD036: false                  # Emphasis used instead of a heading
 MD041: false                  # First line in file should be a top level heading, PULL_REQUEST_TEMPLATE.md is an exception
+MD051: false                  # Link fragments: docs use python-markdown attr_list anchors ({ #fr1 }) that markdownlint can't resolve; Test-DocumentationLink.ps1 validates fragments instead
 MD060: false                  # Table column style — content mixes compact and aligned tables
 
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