ci: drop v5 `all:` composition from labeler.yml (#21627)

actions/labeler@v6 removed the `all:` / `any:` composition keys.
The `server/webui` and `server` entries used `all:` to combine
`any-glob-to-any-file` with negated `all-globs-to-all-files`,
which now errors on every PR with:

    Unknown config options were under "changed-files": all

Flatten both entries to a single `any-glob-to-any-file`. PRs
touching both webui and other server files will now receive both
labels instead of only `server/webui`.

Co-authored-by: Marxist-Leninist <noreply@users.noreply.github.com>