Add set -o pipefail to script that builds iOS E2E version

[mokagio]

What?

Addresses a dumb oversight on my end in #54079. I piped output without accounting for the script returning with the pipe status code instead of that of the piped command.

Why?

Without it, we'd get false positives in the mobile CI pipeline.

How?

set -o pipefail 🤦‍♂️

Testing Instructions

Notice how a CI build with this change fails:

While one without it passes:

Testing Instructions for Keyboard

N.A.

Screenshots or screencast

N.A.

[mokagio]

I considered adding this in the code path where the output is piped, but it seemed better to set it as an option for the whole script instead.

[mokagio]

Also, I didn't make it part of the shebang because of the following ShellCheck warning: On most OS, shebangs can only specify a single parameter. [SC2096]

[github-actions]

Flaky tests detected in 2a8bb4f.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/6105053119
📝 Reported issues:

• [Flaky Test] Should NOT load the view script if the lightbox is disabled in theme.json and in block settings #53802 in /test/e2e/specs/editor/various/behaviors.spec.js

[derekblank]

I observed the differences between the true failing build and the false positive build (and learned about the pipebuild option in the process). LGTM. 🚀