rust_uprev: Fix type information so that mypy runs successfully

BUG=None
TEST=mypy rust_tools/rust_uprev.py && ./run_tests_for rust_tools/rust_uprev.py

Change-Id: Ifdb515aae078b2d35145b80084ecd4f59f498471
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/4760606
Reviewed-by: George Burgess <gbiv@chromium.org>
Commit-Queue: Bob Haarman <inglorion@chromium.org>
Tested-by: Bob Haarman <inglorion@chromium.org>
2 files changed