Declare a generated file that was added after 3.6.1

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/.gitignore b/tests/.gitignore
index 870fa79..0c58875 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -18,6 +18,7 @@
 
 ###START_GENERATED_FILES###
 # Generated source files
+/opt-testcases/tls13-compat.sh
 /suites/*.generated.data
 /suites/test_suite_config.mbedtls_boolean.data
 /suites/test_suite_config.psa_boolean.data