Reverts "Remove bringup:true from Linux tool_tests_widget_preview_scaffold (#166687)" (#166700)

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Reverts: flutter/flutter#166687
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Initiated by: matanlurey
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Reason for reverting: Broke postsubmit ("... not up to date")


https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8718230395584699185/+/u/run_test.dart_for_tool_tests_shard_and_subshard_widget_preview_scaffold/stdout
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Original PR Author: bkonyi
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Reviewed By: {matanlurey}
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This change reverts the following previous change:
New shard seems to be stable and passing consistently.
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Co-authored-by: auto-submit[bot] <flutter-engprod-team@google.com>

.ci.yaml

@@ -1592,6 +1592,7 @@ targets:
   - name: Linux tool_tests_widget_preview_scaffold
     recipe: flutter/flutter_drone
     timeout: 60
+    bringup: true
     properties:
       add_recipes_cq: "true"
       dependencies: >-