files are re-downloaded after fixing hash

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Checklist

• I agree to follow the Code of Conduct that this project adheres to.
• I have searched the issue tracker for a bug that matches the one I want to file, without success.

flatpak-builder version

flatpak-builder 1.4.1

Flatpak version

Flatpak 1.14.8

How to reproduce

1. write a module definition that has the "sha256" property empty or wrong
2. see error: Failed to download sources: module example-module: Wrong sha256 checksum for file.tar.gz, expected "...", was "..."
3. fix the sha256 in the manifest

Expected Behavior

uses already downloaded file

Actual Behavior

downloads huge file again

Additional Information

No response