Fix 1-variant fallback issue in aconfig_test.go

This was missed earlier because it was not setup to run on an
m nothing --no-skip-soong-tests

Bug: 372091092
Test: m nothing --no-skip-soong-tests with aosp/3318965
Change-Id: I0f0c0ed2dbe4546aef954198ef63603ed3e3af8a
diff --git a/apex/Android.bp b/apex/Android.bp
index 4848513..0e2f564 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -33,6 +33,7 @@
         "vndk.go",
     ],
     testSrcs: [
+        "aconfig_test.go",
         "apex_test.go",
         "bootclasspath_fragment_test.go",
         "classpath_element_test.go",