fix: WorkspaceType admission rejecting forward-referenced APIExports

[pen-pal]

Summary

Fixes a regression in 0.31.2 where creating a WorkspaceType referencing an APIExport that doesn't exist yet is rejected with no permission to bind to export ..., even for admins.

The bind-permission check (added in #4082) treats a NotFound on the APIExport lookup the same as a permission denial. This breaks the common flow of creating a WorkspaceType before its APIExports.

Now: if the APIExport isn't found, skip the SAR for that entry. The check still runs whenever the APIExport exists.

What Type of PR Is This?

/kind bug
/kind regression

Related Issue(s)

Fixes #4145

Release Notes

Fix a regression in WorkspaceType admission that rejected creates referencing an APIExport that did not yet exist, even for admins. Such forward references are allowed again; the bind-permission check still applies when the APIExport exists.

[kcp-ci-bot]

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