chore(ci): Set up Depot CLI for E2E if required

[khvn26]

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Changes

Fixes the following failure when running E2E against images in ephemeral mode:

Run depot pull-token | docker login -u x-token --password-stdin registry.depot.dev
/home/runner/work/_temp/735[4](https://github.com/Flagsmith/flagsmith/actions/runs/9663743858/job/26656781703#step:4:5)36f3-00ef-4984-a7c6-e8c5ac5caba8.sh: line 1: depot: command not found
Error: Cannot perform an interactive login from a non TTY device
Error: Process completed with exit code 1.

How did you test this code?

This is a CI change.

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3 Ignored Deployments

| Name | Status | Preview | Comments | Updated (UTC) | | :--- | :----- | :------ | :------- | :------ | | **docs** | ⬜️ Ignored ([Inspect](https://vercel.com/flagsmith/docs/3SH4pbJ1zwoko9X1V5xWuX7T7jFD)) | | | Jun 25, 2024 2:54pm | | **flagsmith-frontend-preview** | ⬜️ Ignored ([Inspect](https://vercel.com/flagsmith/flagsmith-frontend-preview/FTcXSQCYcRCWq85rZhEx1ZfW8wDY)) | | | Jun 25, 2024 2:54pm | | **flagsmith-frontend-staging** | ⬜️ Ignored ([Inspect](https://vercel.com/flagsmith/flagsmith-frontend-staging/GrKYdtv7VLC6Z2U9WLUxxgTkqmUg)) | | | Jun 25, 2024 2:54pm |

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 96.57%. Comparing base (b9a6f92) to head (031e833). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4229 +/- ## ======================================= Coverage 96.57% 96.57% ======================================= Files 1190 1190 Lines 38754 38754 ======================================= Hits 37426 37426 Misses 1328 1328 ```

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