Allow getJSON errors to be ignored

This change is mostly motivated to get a more stable CI build (we're building the Hugo site there, with Instagram and Twitter shortcodes sometimes failing).

Fixes #7866

markup/converter/converter.go

@@ -31,7 +31,7 @@ type ProviderConfig struct {
 
 	Cfg       config.Provider // Site config
 	ContentFs afero.Fs
-	Logger    *loggers.Logger
+	Logger    loggers.Logger
 	Highlight func(code, lang, optsStr string) (string, error)
 }