Fix -Wrange-loop-construct warning

Fixing these warnings either by adding a reference to the loop index's
type or removing the reference from it.

frameworks/native/libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp:260:21:
error: loop variable 'service' creates a copy from type
'android::String16 const' [-Werror,-Wrange-loop-construct]
  260 |     for (const auto service : services) {
      |                     ^
frameworks/native/libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp:260:10:
note: use reference type 'android::String16 const &' to prevent copying
  260 |     for (const auto service : services) {
      |          ^~~~~~~~~~~~~~~~~~~~
      |                     &

Bug: 153747076
Test: m & presubmits
Flag: EXEMPT refactor
Change-Id: I0efa171c1685b883b31116626c7579b4f91e802a