[tool] Fixes crash in tools/minidump.py
[tool] Fixes crash in tools/minidump.py

Fixed by migrating to dict.items() which is available in both python2
and python3.

TEST=Manual testing in python2 and python3.

Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-win-release-x64-try
Bug: https://github.com/dart-lang/sdk/issues/46029
Change-Id: I1c8363dfc44dc39f2430f84c4f22631a2e7203cd
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/200184
Reviewed-by: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@google.com>
Commit-Queue: Clement Skau <495593248b6158163719b90dde8357b589c8e5d0@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk