ci: Reinstate `--depth=1000` in cloning Flutter, once Flutter has a new tag

[chrisbobbe]

Flutter main now has well over a thousand commits since the most recent tag:

diff --git pubspec.yaml pubspec.yaml
index 780c05765..c021e8d1e 100644
--- pubspec.yaml
+++ pubspec.yaml
@@ -14,8 +14,8 @@ environment:
   # We use a recent version of Flutter from its main channel, and
   # the corresponding recent version of the Dart SDK.
   # Feel free to update these regularly; see README.md for instructions.
-  sdk: '>=3.7.0-224.0.dev <4.0.0'
-  flutter: '>=3.28.0-1.0.pre.35'  # 1c1f35711be76d1d2a9f5e3a730747591e64e14a
+  sdk: '>=3.7.0-267.0.dev <4.0.0'
+  flutter: '>=3.28.0-2.0.pre.38575'  # 65ff060283e19423e9538c18c24e44495b70aeff
 
 # To update dependencies, see instructions in README.md.
 dependencies:

These are migrated engine commits from the merge of flutter/engine into the flutter/flutter monorepo.

Anyway, when we do a shallow clone with --depth=1000, CI can't see the most recent tag, which is needed:

      # […] we need the most recent tag
      # so that Flutter knows its version and sees the constraint in our
      # pubspec is satisfied. […]

So we'll be temporarily removing the --depth=1000, to do a full clone instead of a shallow clone. See discussion: #1184 (comment)

That change will slow down CI, so this issue is to reinstate the --depth=1000 once Flutter makes a new tag.