bin/lint-markdown: Only run against git-tracked markdown files (#780)

Rather than maintaining effectively another ignore list, use the one we
already have via git. This also adapts better to usage in child
projects, as they will likely have more language/project specific
locations to ignore that we can't realistically maintain in this parent
template.

bin/lint-markdown

@@ -18,6 +18,5 @@ else
     link_check_cmd="npx markdown-link-check"
 fi
 
-# Recursively find all markdown files (*.md) in the current directory, excluding node_modules and .venv subfolders.
-# Pass them in as args to the lint command using the handy `xargs` command.
-find . -name \*.md -not -path "*/node_modules/*" -not -path "*/.venv/*" -not -path "*/.terraform/*" -print0 | xargs -0 -I{} sh -c "${link_check_cmd} --quiet --config ${link_check_config} {}"
+# Run the linter against each markdown file that's tracked in git
+git ls-files -z '*.md' | xargs -0 -I{} sh -c "${link_check_cmd} --quiet --config ${link_check_config} {}"