Add package:file to DEPS

[dcharkes]

https://dart-review.googlesource.com/c/sdk/+/174382 added package:file to the DEPS in Dart.

In order to prevent these manual DEPS file fixes in the future, we should make https://github.com/flutter/buildroot/blob/master/tools/dart/create_updated_flutter_deps.py deal with new dependencies. (Tracked in flutter/flutter#71474.)

Description

Adds package:file to the DEPS file, in correspondence to https://dart-review.googlesource.com/c/sdk/+/174382.

Related Issues

Failing Dart Flutter HHH build: https://ci.chromium.org/ui/p/dart/builders/ci.sandbox/flutter-engine-linux/12295/overview

Tests

No new tests, this fixes the build.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]). This will ensure a smooth and quick review process.

• I read the contributor guide and followed the process outlined there for submitting PRs.
• I signed the CLA.
• I read and followed the C++, Objective-C, Java style guides for the engine.
• I read the tree hygiene wiki page, which explains my responsibilities.
• I updated/added relevant documentation.
• All existing and new tests are passing.
• I am willing to follow-up on review comments in a timely manner.

Reviewer Checklist

• I have submitted any presubmit flakes in this PR using the engine presubmit flakes form before re-triggering the failure.

Breaking Change

Did any tests fail when you ran them? Please read handling breaking changes.

• No, no existing tests failed, so this is not a breaking change.

[dcharkes]

Make sure your PR passes all the pre-commit tests.

Wait for Cirrus to give the green light before merging a PR. Cirrus runs a bunch of pre-commit checks

The Linux Android Scenarios bot is consistently infra failing.

Running from /b/s/w/ir/cache/builder/src/flutter/testing/scenario_app/android/gradle-home/bin/bin/python
Copying file:///b/s/w/ir/k/recipe_cleanup/tmpHunuG3/diff_failures.zip [Content-Type=application/zip]...
/ [0 files][    0.0 B/  1.0 MiB]                                                
AccessDeniedException: 403 flutter-try-builder@chops-service-accounts.iam.gserviceaccount.com does not have storage.objects.create access to flutter_infra/flutter//diff_failures.zip.

[fluttergithubbot]

This pull request is not suitable for automatic merging in its current state.

• The status or check suite Linux Android Scenarios has failed. Please fix the issues identified (or deflake) before re-applying this label.

[dcharkes]

The infra failure is the last step of Linux Android Scenarios, and does not indicate a problem with this CL.

This CL restores HHH and Golem coverage, so we're landing this despite Linux Android Scenarios not being green.