Bump package:file (#6522)

Prep for https://github.com/flutter/flutter/pull/136418.

The `flutter/tests` integration is working :)

packages/devtools_app/pubspec.yaml

diff --git a/packages/devtools_app/pubspec.yaml b/packages/devtools_app/pubspec.yaml
index c4174eb..0d11509 100644
--- a/packages/devtools_app/pubspec.yaml
+++ b/packages/devtools_app/pubspec.yaml
@@ -28,7 +28,7 @@
   devtools_app_shared: ^0.0.5
   devtools_extensions: ^0.0.8
   devtools_shared: ^4.0.1
-  file: ^6.0.0
+  file: ">=6.0.0 <8.0.0"
   file_selector: ^0.8.0
   file_selector_linux: ^0.0.2
   file_selector_macos: ^0.0.2