Add empty vf-intro_subheading

src/site/partners/index.njk

@@ -34,6 +34,7 @@ embl_content_meta_properties:
     "theme": "primary"
   },
   "vf_intro_heading": title,
+  "vf-intro__subheading": "",
   "vf_intro_lede": subtitle+"",
   "vf_intro_text": [
       "Please understand that EMBL cannot take any responsibility for the content of websites of the partner organisations nor for aspects of the jobs offered by them. Employment conditions for these positions are subject to the regulations applicable within the partner organisations.",