gitignore: ignore test_keys.h and test_certs.h

These files are automatically generated at build time so they
do not need to be tracked.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/tests/.gitignore b/tests/.gitignore
index 973ebb5..838ea69 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -21,4 +21,6 @@
 /suites/*.generated.data
 /suites/test_suite_psa_crypto_storage_format.v[0-9]*.data
 /suites/test_suite_psa_crypto_storage_format.current.data
+/src/test_keys.h
+/src/test_certs.h
 ###END_GENERATED_FILES###