Add files installed to root to diff allowlist

system.img is built from both $OUT/system and $OUT/root. As the diff
tool doesn't check $OUT/root, this change temporarily adds two files
under root (adb_keys and init.environ.rc) to allowlist. They will be
removed once the diff tool is fixed.

Bug: 351258461
Test: build
Change-Id: I0f24dcae67c72be5619a86f6f025ec8bcb146084