Update references to old Github organisation

Replace references to ARMmbed organisation with the new
org, Mbed-TLS, following project migration.

Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index 82d1573..10a7f81 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -12,7 +12,7 @@
 
 /* Needed only for test case data under #if defined(MBEDTLS_USE_PSA_CRYPTO),
  * but the test code generator requires test case data to be valid C code
- * unconditionally (https://github.com/ARMmbed/mbedtls/issues/2023). */
+ * unconditionally (https://github.com/Mbed-TLS/mbedtls/issues/2023). */
 #include "psa/crypto.h"
 
 #define RSA_KEY_SIZE 512