(filezilla) Fixes DownloadPage Request

Description

This updates the Invoke-WebRequest used in the Filezilla update script to find the versions to add an accept header.

The filezilla update was failing due to an invalid version.

On investigation, the returned page had no useful content. This change fixes that, and allows us to continue grabbing updated links.

Before changes:

After changes:

[x] Bug fix (non-breaking change which fixes an issue)
~[ ] New feature (non-breaking change which adds functionality)~
~[ ] Breaking change (fix or feature that would cause existing functionality to change)~
~[ ] Migrated package (a package has been migrated from another repository)~

[x] My code follows the code style of this repository.
~[ ] My change requires a change to documentation (this usually means the notes in the description of a package).~
~[ ] I have updated the documentation accordingly (this usually means the notes in the description of a package).~
~[ ] I have updated the package description and it is less than 4000 characters.~
[ ] All files are up to date with the latest Contributing Guidelines
[ ] The added/modified package passed install/uninstall in the Chocolatey Test Environment(https://github.com/chocolatey-community/chocolatey-test-environment/). Note that we don't support the use of any other environment.
[x] The changes only affect a single package (not including meta package).