fix: processNodeUrl for srcset

[patak-dev]

Closes #14744

Description

See newly added test, we were doing url tests on the srcset value:

  <img
    class="img-src-set-mixed"
    src="/icon.png"
    srcset="https://vitejs.dev/logo-with-shadow.png 1x, ./nested/asset.png 2x"
    alt=""
  />

It only worked so far because normally all the URLs in srcset will be of the same type (in src, or in public, or external)

The new test is failing during build, I added a condition and a TODO to fix that in another PR.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[sapphi-red]

LGTM

Does this fix #14744? It looks a bit different.

[patak-dev]

It should fix it after #14774 and this PR (for dev), we can ask for an issue with a proper reproduction if not.

See blu's review