Update shortcodes-and-filters.yml to add table-cell-merge (#1962)

(cherry picked from commit a8d8b06)

Author: herosi

docs/extensions/listings/shortcodes-and-filters.yml

@@ -698,6 +698,12 @@
   description: >
     Quarto Extension for Automatic Language Tabs
 
+- name: table-cell-merge
+  path: https://github.com/herosi/table-cell-merge
+  author: '[Hiroshi Suzuki](https://github.com/herosi)'
+  description: >
+    Enable `colspan` and `rowspan` in Markdown tables.
+
 - name: tachyons
   path: https://github.com/gadenbuie/quarto-tachyons
   author: '[Garrick Aden-Buie](https://github.com/gadenbuie)'