tools: patch: Fix build by not modifing Makefile.am

tools: patch: Fix build by not modifing Makefile.am

A new test case was adding in one of the patches fixing a problem, this
also included a change in the test/Makefile.am to add this test case.
The build system detected a change in the Makefile.am and wants to
regenerate the Makefile.in, but this fails because automake-1.15 is not
installed yet. As automake depends on patch being build first, make sure
we do not modify the Makefile.am.

This fixes build problem seen by the build bots.

Fixes: 4797dddfde6 ("patch: apply upstream cve fixes")
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
(backported from 759f111f8d7f2d9f5f12713fc6f48ce6422997ec)