🦺(frontend) check content type pdf on PdfBlock

Pdfblock was quite permissive on the content type
it was accepting. Now it checks that the content
type is exactly 'application/pdf' before rendering
the PDF viewer.

CHANGELOG.md

@@ -15,6 +15,10 @@ and this project adheres to
 
 - 🥅(frontend) intercept 401 error on GET threads #1754
 
+## Changed
+
+- 🦺(frontend) check content type pdf on PdfBlock #1756
+
 ### Fixed
 
 - 🐛(frontend) fix tables deletion #1752