Correct standbycheck regression test output.

Commit 2eb34ac3 changed error messages emit when commands are
rejected during recovery. But it forgot to update the standbycheck
regression test output with those error message changes.

Reported-by: Michail Nikolaev
Author: Michail Nikolaev
Reviewed-by: Fujii Masao
Discussion: https://postgr.es/m/CANtu0ojFPgcspH=0nNZ+qmu0XD69sXKtVttuSoYKHawRADSQGg@mail.gmail.com

src/test/regress/expected/hs_standby_disallowed.out

@@ -64,7 +64,7 @@ SELECT count(*) FROM hs1;
 (1 row)
 
 COMMIT PREPARED 'foobar';
-ERROR:  COMMIT PREPARED cannot run inside a transaction block
+ERROR:  cannot execute COMMIT PREPARED during recovery
 ROLLBACK;
 BEGIN;
 SELECT count(*) FROM hs1;
@@ -86,7 +86,7 @@ SELECT count(*) FROM hs1;
 (1 row)
 
 ROLLBACK PREPARED 'foobar';
-ERROR:  ROLLBACK PREPARED cannot run inside a transaction block
+ERROR:  cannot execute ROLLBACK PREPARED during recovery
 ROLLBACK;
 -- Locks
 BEGIN;