Downgrade to electron 20.3.4 to fix crash on call hangup

[dbkr]

Fixes element-hq/element-web#23783

Choose either this or #460

Checklist

• Ensure your code works with manual testing
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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Here's what your changelog entry will look like:

🐛 Bug Fixes

• Downgrade to electron 20.3.4 to fix crash on call hangup (#459). Fixes Element white-screen-of-deaths when I hang up a Matrix-native 1:1 call element-web#23783.

[t3chguy]

Does 21 not fix this? Is there any upstream issue?

[robintown]

I'd also like to know if we could upgrade

[dbkr]

I didn't test as I assumed a major update of electron would be out of the question for a last minute release pre-release patch, but yes, just tested 21.3.0 and that's fine too. Doesn't look like any of the breaking changes would be relevant. Have PRed that in #460 so you can choose your own adventure.

[robintown]

I guess if we could merge this to the release branch, and #458 to the develop branch, that'd be best

[t3chguy]

Luckily this repo is quiet enough that it didn't need rebasing :D