fix: source.unsplash.com/random was deprecated in 2024 (now 503s)

[kiluazen]

extensions/amp-accordion/1.0/README.md references the deprecated source.unsplash.com/random endpoint, which Unsplash retired in mid-2024 and which now returns HTTP 503 instead of an image.

---

Why this is needed

source.unsplash.com/random (and the related source.unsplash.com/featured) was deprecated by Unsplash in mid-2024 and the endpoint now returns HTTP 503 instead of an image. Browsers render a broken-image icon in place of the intended visual.

Verify in any shell:

curl -sI https://source.unsplash.com/random/800x600?office | head -1
# HTTP/1.1 503 Service Unavailable

What this PR changes

Updates the amp-accordion 1.0 README example's image URL so the Section 3 accordion example renders a real image (not a 503 broken-image icon) for anyone copy-pasting the example into their AMP project.

Replacement details

picsum.photos accepts the same /<W>/<H> path shape and requires no API key / auth. Dimensions (320×256) preserved verbatim. This is a docs-only change — no extension behaviour is affected.

Background

I'm tracking the deprecated source.unsplash.com/random endpoint across public repos as part of tteg, a tiny CLI/HTTP API I built so projects can drop in real Unsplash photos without registering an Unsplash app or managing API keys. tteg isn't introduced as a dependency by this PR — the diff is dependency-free picsum.photos. But if you want topic-matched real photos as a follow-up, the no-key HTTP API is at https://tteg-api-53227342417.asia-south1.run.app/search?q=<query>&n=1 (CORS-on, no auth).

One extra artifact you may find handy: a public scanner at https://tteg.kushalsm.com/scan?url= that highlights this same broken-URL pattern in any landing page — useful for verifying the fix lands and for finding other places source.unsplash.com/random slipped in. Source: https://github.com/kiluazen/tteg-landing/blob/main/scan.html.

Research note covering ~16,500 files across ~885 unique repos that still hotlink the deprecated endpoint: https://github.com/kiluazen/tteg/blob/research-note-autark/RESEARCH.md.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}