ci: fix the index spec path in CODEOWNERS

[dajiaohuang]

The index specification moved from docs/src/format/table/index/ to
docs/src/format/index/, but this CODEOWNERS entry still named the old path,
so it matched no tracked file. The 21 files under docs/src/format/index/
were left without a review request, unlike the file and table specs, whose
patterns still resolve.

$ git ls-tree -r --name-only HEAD -- docs/src/format/table/index/ | wc -l
0
$ git ls-tree -r --name-only HEAD -- docs/src/format/index/ | wc -l
21

The other patterns are unaffected: protos/index.proto and
protos/index_old.proto still exist, and docs/src/format/file/ (4 paths)
and docs/src/format/table/ (10 paths) still resolve.

Checked: every pattern in the file now matches at least one tracked path, and
the typos pre-commit hook passes on the changed file. The change touches no
Rust or Python surface, so no language lint applies.

[lance-gatekeeper]

❌ Gate recommendation: request changes.

The direct path correction is the right mechanism, but GitHub still rejects the index owner, so this revision cannot deliver the spec-review contract established in #5858. Use a repository-valid owner on this rule and verify that GitHub reports no CODEOWNERS error for it.

[lance-gatekeeper]

GitHub still reports this changed rule as Unknown owner, so no review request will be sent for the 21 index-spec paths even though the path now matches. Point the rule at an owner GitHub accepts for this repository (for example, the intended organization/team slug if that team exists and has write access), then verify this line disappears from the CODEOWNERS error report.

Reproducer

gh api --method GET repos/lance-format/lance/codeowners/errors \
  -f ref=d981fd51e45223fc3833f92fcfef22afb5eba50e \
  --jq '.errors[] | select(.line == 14) | {line, kind, source}'

Observed:

{"kind":"Unknown owner","line":14,"source":"docs/src/format/index/ @index-spec-team\n"}

Expected: no error for line 14.

[dajiaohuang]

I checked the live CODEOWNERS validation for commit d981fd5. GitHub reports Unknown owner for @file-spec-team, @table-spec-team, and @index-spec-team (including the corrected docs/src/format/table/index/ rule), so the remaining blocker is the owner identities rather than the path. I do not have org-admin/team visibility to choose a repository-valid replacement. Please provide the valid team or maintainer username for the index-spec rule and I can update the PR.

[lance-gatekeeper]

❌ Gate recommendation: request changes.

The author’s follow-up confirms the validator result and clarifies that selecting a repository-valid index owner requires maintainer input. The path correction is still right, but the spec-review contract established in #5858 remains unmet until a maintainer identifies the intended writable team or user and the changed rule is updated so GitHub reports no CODEOWNERS error.