Add unit & widget tests for `save_page_dialog.dart`

[may-tas]

Is your feature request related to a problem? Please describe.

• Current code coverage is very low and needs immediate attention. We must develop thorough tests for several files to ensure reliability and functionality.

Describe the solution you'd like

• Write unit and widget tests for save_page_dialog.dart

Additional context

• Please follow the existing testing pattern used in the main codebase.

[github-actions]

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[GitMasterJatin]

Please assign me this issue