Add test case for root with max_pathlen=0

This was already working but not tested so far

(Test case from previous commit still failing.)

Test certificates generated with:

programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert91.key
programs/pkey/gen_key type=ec ec_curve=secp256r1 filename=cert92.key

programs/x509/cert_write serial=91 output_file=cert91.crt is_ca=1 \
    issuer_key=cert91.key issuer_name="CN=Root 9,O=mbed TLS,C=UK" \
    selfsign=1 max_pathlen=0
programs/x509/cert_write serial=92 output_file=cert92.crt \
    issuer_key=cert91.key issuer_name="CN=Root 9,O=mbed TLS,C=UK" \
    subject_key=cert92.key subject_name="CN=EE 92,O=mbed TLS,C=UK"

mv cert9?.crt tests/data_files/dir4
rm cert9?.key
diff --git a/tests/suites/test_suite_x509parse.data b/tests/suites/test_suite_x509parse.data
index 5d9311c..2f2137f 100644
--- a/tests/suites/test_suite_x509parse.data
+++ b/tests/suites/test_suite_x509parse.data
@@ -1160,10 +1160,14 @@
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_RSA_C
 mbedtls_x509_crt_verify_chain:"data_files/dir4/cert61.crt data_files/dir4/cert63.crt data_files/dir4/cert62.crt":"data_files/dir4/cert61.crt":0
 
-X509 CRT verify chain #9 (self signed maxpathlen root)
+X509 CRT verify chain #9 (zero pathlen first intermediate, valid)
 depends_on:MBEDTLS_SHA256_C:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
 mbedtls_x509_crt_verify_chain:"data_files/dir4/cert83.crt data_files/dir4/cert82.crt":"data_files/dir4/cert81.crt":0
 
+X509 CRT verify chain #10 (zero pathlen root, valid)
+depends_on:MBEDTLS_SHA256_C:MBEDTLS_ECDSA_C:MBEDTLS_ECP_DP_SECP256R1_ENABLED
+mbedtls_x509_crt_verify_chain:"data_files/dir4/cert92.crt":"data_files/dir4/cert91.crt":0
+
 X509 OID description #1
 x509_oid_desc:"2B06010505070301":"TLS Web Server Authentication"