binder: Disable flaky SecurityPolicy tests

Not using `@Ignore` because the tests can probably run successfully
under Bazel.

See #8391

binder/build.gradle

@@ -13,6 +13,8 @@ android {
                 srcDirs += "${projectDir}/../core/src/test/java/"
                 setIncludes(["io/grpc/internal/FakeClock.java",
                              "io/grpc/binder/**"])
+                exclude 'io/grpc/binder/ServerSecurityPolicyTest.java'
+                exclude 'io/grpc/binder/SecurityPoliciesTest.java'
             }
         }
         androidTest {