lisp/ox-md.el (org-md--footnote-section): Honor `org-md-toplevel-hlevel'

* testing/lisp/test-ox-md.el (ox-md/footnotes-level): New test file
and new test for the bug.

Reported-by: Pablo Padilla <pgpb.padilla@gmail.com>
Link: https://orgmode.org/list/AC5BC3B4-33F9-487E-877E-EA9A829608A5@gmail.com

lisp/ox-md.el

@@ -305,7 +305,7 @@ INFO is a plist used as a communication channel."
          (section-title (org-html--translate "Footnotes" info)))
     (when fn-alist
       (format (plist-get info :md-footnotes-section)
-              (org-md--headline-title headline-style 1 section-title)
+              (org-md--headline-title headline-style (plist-get info :md-toplevel-hlevel) section-title)
               (mapconcat (lambda (fn) (org-md--footnote-formatted fn info))
                          fn-alist
                          "\n")))))

testing/lisp/test-ox-md.el

@@ -0,0 +1,43 @@
+;;; test-ox-md.el --- Tests from ox-md.el            -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2023  Ihor Radchenko
+
+;; Author: Ihor Radchenko <yantar92@posteo.net>
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Code:
+
+(require 'ox-md)
+
+(ert-deftest ox-md/footnotes-level ()
+  "Test `org-md-toplevel-hlevel' being honored by footnote section."
+  (org-test-with-temp-text "
+** level 1
+   Post starts here. [fn:1]
+*** level2
+    lorem ipsum
+** Footnotes
+[fn:1] a footnote 
+"
+    (let ((org-md-toplevel-hlevel 4)
+          (export-buffer "*Test MD Export*")
+          (org-export-show-temporary-export-buffer nil))
+      (org-export-to-buffer 'md export-buffer)
+      (with-current-buffer export-buffer
+        (goto-char (point-min))
+        (should (search-forward "#### Footnotes"))))))
+
+(provide 'test-ox-md)
+;;; test-ox-md.el ends here