[Meta] Fix i18n end-to-end test

[arctic-hen7]

For about a year now, the i18n end-to-end test has been extremely patchy, and, since GHA automatically stops other test runs if one fails, it's not uncommon for a PR or commit to get failing tests even if it's perfectly valid, just because the i18n test fails. Others have failed in the past (false negatives are an unavoidable side-effect of full headless browser end-to-end tests, I get that), but none as frequently as the i18n one (to my observation).

In terms of fixing this, I think the first step is to try to get GHA to push ahead and run all the tests, even if a few fail, which would also provide far better debugging capability, and make re-runs much speedier (we usually just re-run failing tests, and if there's only one rather than 14 others that were cancelled, that's much quicker!). Beyond that, I'll have a look in the coming days at any possible improvements that could be made to the test itself to prevent the weird failure.

TODO actual error log when I have time to extract it from GHA

[github-actions]

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[arctic-hen7]

Error log:

---- main stdout ----
thread 'main' panicked at 'assertion failed: `(left == right)`
  left: `""`,
 right: `"Hello, \u{2068}User\u{2069}!"`', examples/core/i18n/tests/main.rs:16:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[arctic-hen7]

Also, this is less inconvenient now that the matrix is set up to not fail-fast, meaning everything is run anyway so we can actually see exactly what failed each time.

[arctic-hen7]

Noting that I haven't seen this bug since capsules were merged, so I may have fixed something at some stage accidentally...closing very tentatively for now...

[arctic-hen7]

Well, that was predictable.