audit: fix FormulaText match

It's used in `audit_text`

Closes Homebrew/homebrew#37139.

Signed-off-by: Xu Cheng <xucheng@me.com>

Library/Homebrew/cmd/audit.rb

@@ -69,6 +69,14 @@ class FormulaText
   def has_trailing_newline?
     /\Z\n/ =~ @text
   end
+
+  def =~ regex
+    regex =~ @text
+  end
+
+  def !~ regex
+    regex !~ @text
+  end
 end
 
 class FormulaAuditor