modules: Update tf-m-tests for picolibc

This module also needs some small changes to build with picolibc.

This has not been merged to the Zephyr tf-m-tests repository yet,
that PR is:

zephyrproject-rtos/tf-m-tests#17

Signed-off-by: Keith Packard <keithp@keithp.com>

Author: keith-packard

west.yml

@@ -370,7 +370,7 @@ manifest:
       groups:
         - debug
     - name: tf-m-tests
-      revision: a90702bcb8fadb6f70daf0ffbb13888dfe63fc99
+      revision: pull/17/head
       path: modules/tee/tf-m/tf-m-tests
       groups:
         - testing