audit: allow env :std in custom taps.

This is a nicer experience than writing `Requirement`s by hand.

Library/Homebrew/dev-cmd/audit.rb

@@ -304,7 +304,7 @@ class FormulaAuditor
   def audit_formula_name
     return unless @strict
     # skip for non-official taps
-    return if formula.tap.nil? || !formula.tap.official?
+    return unless formula.tap&.official?
 
     name = formula.name
 
@@ -718,7 +718,13 @@ class FormulaAuditor
 
     return unless @strict
 
-    problem "`#{Regexp.last_match(1)}` in formulae is deprecated" if line =~ /(env :(std|userpaths))/
+    if formula.tap&.official? && line.include?("env :std")
+      problem "`env :std` in official tap formulae is deprecated"
+    end
+
+    if line.include?("env :userpaths")
+      problem "`env :userpaths` in formulae is deprecated"
+    end
 
     if line =~ /system ((["'])[^"' ]*(?:\s[^"' ]*)+\2)/
       bad_system = Regexp.last_match(1)