lint: ignore files ignored by git in mlc

Updating to MLC v0.18.0 includes a new feature which will ignore all
files ignored by git: `--gitignore`.

This helps avoid false-positives flagged by this linter in non-project
files, such as a developer might expect to have in their directory (e.g.
guix-builds, python venvs, etc.)

ci/lint/04_install.sh

@@ -58,7 +58,7 @@ curl -sL "https://github.com/koalaman/shellcheck/releases/download/${SHELLCHECK_
     tar --xz -xf - --directory /tmp/
 mv "/tmp/shellcheck-${SHELLCHECK_VERSION}/shellcheck" /usr/bin/
 
-MLC_VERSION=v0.16.3
+MLC_VERSION=v0.18.0
 MLC_BIN=mlc-x86_64-linux
 curl -sL "https://github.com/becheran/mlc/releases/download/${MLC_VERSION}/${MLC_BIN}" -o "/usr/bin/mlc"
 chmod +x /usr/bin/mlc

test/lint/test_runner/src/main.rs

@@ -410,6 +410,7 @@ fn lint_markdown() -> LintResult {
         "--offline",
         "--ignore-path",
         md_ignore_path_str.as_str(),
+        "--gitignore",
         "--root-dir",
         ".",
     ])