Fix an epg test for recent GnuPG versions (bug#33439)

* test/lisp/epg-tests.el (epg-decrypt-1):
Tell recent GnuPG (e.g. 2.2.11) not to worry about missing MDC.

test/lisp/epg-tests.el

@@ -87,6 +87,8 @@
 (ert-deftest epg-decrypt-1 ()
   (skip-unless (epg-tests-find-usable-gpg-configuration 'require-passphrase))
   (with-epg-tests (:require-passphrase t)
+    (with-temp-file (expand-file-name "gpg.conf" epg-tests-home-directory)
+      (insert "ignore-mdc-error"))
     (should (equal "test"
 		   (epg-decrypt-string epg-tests-context "\
 -----BEGIN PGP MESSAGE-----