Escaping template variable output

[PR for version 1.3.0.0 to the plugin gallery](https://github.com/pkp/plugin-gallery/pull/343/changes#pullrequestreview-2750948358) raised concerns about this unescaped template variable:

https://github.com/ulsdevteam/inlineHtmlGalley/blob/5af7a008c34eae779212ab892a9a60c5ef4a1c58/templates/blockReferences.tpl#L22

C.f. https://github.com/pkp/bootstrap3/issues/246

