ci: Fetch 3000 commits from upstream, rather than 1000

[gnprice]

Fixes #1710.

This should work around the problem for a few more months. If it doesn't get fixed upstream by then, we can figure something else out.

While we're here, also revert the temp hack we needed for a previous issue:

a3bbee9 ci: Revert temp hack for desync of Flutter main branch

This reverts commits 9cc34cd and 37af86d (#1691, #1690).

The operational issue in the upstream repo which this worked around has been fixed.

[gnprice]

Hmm interesting. CI failed in flutter test, on just 4 tests:

❌ /home/runner/work/zulip-flutter/zulip-flutter/test/widgets/message_list_test.dart: OutboxMessageWithPossibleSender hidden -> waiting (failed)
❌ /home/runner/work/zulip-flutter/zulip-flutter/test/widgets/message_list_test.dart: OutboxMessageWithPossibleSender hidden -> failed, tap to restore message (failed)
❌ /home/runner/work/zulip-flutter/zulip-flutter/test/widgets/message_list_test.dart: OutboxMessageWithPossibleSender hidden -> failed, tapping does nothing if compose box is not offered (failed)
❌ /home/runner/work/zulip-flutter/zulip-flutter/test/widgets/message_list_test.dart: OutboxMessageWithPossibleSender waiting -> waitPeriodExpired, tap to restore message (failed)

The errors look like this:

❌ /home/runner/work/zulip-flutter/zulip-flutter/test/widgets/message_list_test.dart: OutboxMessageWithPossibleSender hidden -> waiting (failed)
  ══╡ EXCEPTION CAUGHT BY IMAGE RESOURCE SERVICE ╞════════════════════════════════════════════════════
  The following NetworkImageLoadException was thrown resolving an image codec:
  HTTP request failed, statusCode: 400, https://chat.example/bar.jpg
  
  When the exception was thrown, this was the stack:
  #0      NetworkImage._loadAsync (package:flutter/src/painting/_network_image_io.dart:130:9)
  <asynchronous suspension>
  #1      MultiFrameImageStreamCompleter._handleCodecReady (package:flutter/src/painting/image_stream.dart:1021:3)
  <asynchronous suspension>
  
  Image provider: NetworkImage("https://chat.example/bar.jpg", scale: 1.0, webHtmlElementStrategy:
    never, headers: {Authorization: Basic
    bWFpbDE0MTlAZXhhbXBsZS5jb206ZFFjRUpXVHEzTGN6b3NEa0puUlR3ZjMxem5pR3ZNck8=, User-Agent:
    ZulipFlutter/1.0.0+1 (Android 13)})
  Image key: NetworkImage("https://chat.example/bar.jpg", scale: 1.0, webHtmlElementStrategy: never,
    headers: {Authorization: Basic
    bWFpbDE0MTlAZXhhbXBsZS5jb206ZFFjRUpXVHEzTGN6b3NEa0puUlR3ZjMxem5pR3ZNck8=, User-Agent:
    ZulipFlutter/1.0.0+1 (Android 13)})
  ════════════════════════════════════════════════════════════════════════════════════════════════════
  Warning: At least one test in this suite creates an HttpClient. When running a test suite that uses
  TestWidgetsFlutterBinding, all HTTP requests will return status code 400, and no network request
  will actually be made. Any test expecting a real network connection and status code will fail.
  To test code that needs an HttpClient, provide your own HttpClient implementation to the code under
  test, so that your test can consistently provide a testable response to the code under test.
  Test failed. See exception logs above.
  The test description was: hidden -> waiting

[gnprice]

I reproduce locally; bisecting to find the upstream change that broke it.

[gnprice]

Those tests broke with upstream commit flutter/flutter@97aae2a (flutter/flutter#171916), merged yesterday.

The reason customer_testing didn't prevent that is that the pin there is 834834b, from early last month. The affected tests were introduced in 11f05dc (#1538) and then 7e29108 (#1453), both a week later.

I'll merge this PR since it clearly does fix #1710, and the remaining issue is something different.