Fix dead download button image link

[hughns]

Pull Request Checklist

• [ ] I read the contributing guide
• [ ] UI change has been tested on both light and dark themes, in portrait and landscape orientations and on iPhone and iPad simulators
• [ ] Accessibility has been taken into account.
• [ ] Pull request is based on the develop branch
• [ ] Pull request contains a changelog file in ./changelog.d
• [ ] You've made a self review of your PR
• [ ] Pull request includes screenshots or videos of UI changes
• [ ] Pull request includes a sign off

[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

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[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: +0.36% :tada:

Comparison is base (344cbec) 12.00% compared to head (9ad04aa) 12.37%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #7682 +/- ## =========================================== + Coverage 12.00% 12.37% +0.36% =========================================== Files 1650 1650 Lines 163849 163849 Branches 67228 67255 +27 =========================================== + Hits 19668 20273 +605 + Misses 143524 142908 -616 - Partials 657 668 +11 ``` | [Flag](https://app.codecov.io/gh/vector-im/element-ios/pull/7682/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | Coverage Δ | | |---|---|---| | [uitests](https://app.codecov.io/gh/vector-im/element-ios/pull/7682/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | `54.97% <ø> (-0.06%)` | :arrow_down: | | [unittests](https://app.codecov.io/gh/vector-im/element-ios/pull/7682/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im) | `6.22% <ø> (+0.35%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im#carryforward-flags-in-the-pull-request-comment) to find out more. [see 18 files with indirect coverage changes](https://app.codecov.io/gh/vector-im/element-ios/pull/7682/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vector-im)

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