Fix bug of unable to suspend packages after reboot

Make copy of an immutable collection before operating on it.

Bug: 408976950
Flag: EXEMPT bugfix
Test: suspend packages with TestDPC, reboot device and try
      suspend / unsuspend again.
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d2b4b028971ced322a7052cfa5c270d6bc9d62d7)
Merged-In: I7b6fe55a0a41d74492579f6f99987fab9467c898
Change-Id: I7b6fe55a0a41d74492579f6f99987fab9467c898