Fix regression in section numbering.

Starting with pandoc 3.1.12, unnumbered sections incremented
the section number.

Closes #9516.

src/Text/Pandoc/Shared.hs

@@ -529,7 +529,7 @@ makeSections numbering mbBaseLevel bs =
           | otherwise = 0
     let newnum = zipWith adjustNum [minLevel..level]
                     (lastnum ++ repeat 0)
-    unless (null newnum) $ S.put newnum
+    unless (null newnum || "unnumbered" `elem` classes) $ S.put newnum
     let (sectionContents, rest) = break (headerLtEq level) xs
     sectionContents' <- go sectionContents
     rest' <- go rest

test/command/9516.md

@@ -0,0 +1,17 @@
+```
+% pandoc --number-sections
+# One {-}
+
+# Two
+
+# Three {-}
+
+# Four
+^D
+<h1 class="unnumbered" id="one">One</h1>
+<h1 data-number="1" id="two"><span
+class="header-section-number">1</span> Two</h1>
+<h1 class="unnumbered" id="three">Three</h1>
+<h1 data-number="2" id="four"><span
+class="header-section-number">2</span> Four</h1>
+```