cmd/update-report: fix formula description display

When on a non-default branch (for e.g., testing), `Formula[formula]` can
return an error. In that case let's silently ignore it.

Library/Homebrew/cmd/update-report.rb

@@ -974,7 +974,11 @@ class ReporterHub
       # Skip non-homebrew/core formulae for security.
       return if formula.include?("/")
 
-      Formula[formula].desc&.presence
+      begin
+        Formula[formula].desc&.presence
+      rescue FormulaUnavailableError
+        nil
+      end
     else
       all_formula_json.find { |f| f["name"] == formula }
                       &.fetch("desc", nil)