Add linker.config.pb test

In apex, ./etc/linker.config.pb file should be readable by linkerconfig.

Bug: 218922042
Test: apex_sepolicy_tests_test
Change-Id: Id41710dc127b5f5bda2d5bbb65271bcc0c5179b1
diff --git a/tests/apex_sepolicy_tests.py b/tests/apex_sepolicy_tests.py
index 2cdde3c..0bcc998 100644
--- a/tests/apex_sepolicy_tests.py
+++ b/tests/apex_sepolicy_tests.py
@@ -105,6 +105,8 @@
     # ./ and apex_manifest.pb
     (Is('./apex_manifest.pb'), AllowRead('file', {'linkerconfig', 'apexd'})),
     (Is('./'), AllowRead('dir', {'linkerconfig', 'apexd'})),
+    # linker.config.pb
+    (Is('./etc/linker.config.pb'), AllowRead('file', {'linkerconfig'})),
 ]