[docs-scanner] Contradictory information about default docker driver support for cache backends

Files:

• content/manuals/build/cache/backends/_index.md
• content/manuals/build/cache/backends/gha.md
• content/manuals/build/cache/backends/registry.md

Issue

The documentation contradicts itself about whether the default docker driver supports certain cache backends.

In _index.md (lines 18-21):

The default docker driver supports the inline, local, registry, and gha cache backends, but only if you have enabled the containerd image store.

In gha.md (lines 11-13):

This cache storage backend is not supported with the default docker driver. To use this feature, create a new builder using a different driver.

In registry.md (lines 15-17):

This cache storage backend is not supported with the default docker driver. To use this feature, create a new builder using a different driver.

Why this matters

A reader trying to use the GitHub Actions cache or registry cache with the default docker driver will get conflicting information:

• The overview page tells them it IS supported (with containerd enabled)
• The specific backend pages tell them it is NOT supported and they must create a new builder

This directly contradicts the reader's ability to determine whether they need to create a new builder or can use their existing default driver.

Suggested fix

Determine which statement is correct:

Option 1: If the default docker driver DOES support these backends with containerd:

• Remove or update the warning in gha.md and registry.md to match _index.md
• Consider adding a note about requiring containerd image store

Option 2: If the default docker driver does NOT support these backends:

• Update _index.md to remove registry and gha from the list of supported backends
• Keep the warnings in the individual backend pages

Note: local.md and inline.md do not have this warning, which is consistent with _index.md saying they are supported.

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Found by nightly documentation quality scanner

Compare the stated driver support in content/manuals/build/cache/backends/_index.md, gha.md, and registry.md, then verify the correct behavior for the default Docker driver with the containerd image store. Update the affected documentation so the overview and backend pages agree and clearly state whether a separate builder is required.