`cargo doc` ci failed in latest `rust version 1.81.0-nightly (cc8da78a0 2024-07-04)`

[Rachelint]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

ci failed in rust version 1.81.0-nightly (cc8da78a0 2024-07-04).
see #6006

Describe the solution you'd like

Fix it.

Describe alternatives you've considered

Additional context

[alamb]

Example failure:

https://github.com/apache/arrow-rs/actions/runs/9807403342/job/27081102878?pr=6006

 Documenting arrow-flight v52.1.0 (/__w/arrow-rs/arrow-rs/arrow-flight)
error: unresolved link to `flightsql`
   --> arrow-flight/src/sql/metadata/sql_info.rs:137:61
    |
137 | /// Handles creating the dense [`UnionArray`] described by [flightsql]
    |                                                             ^^^^^^^^^ no item named `flightsql` in scope
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
    = note: `-D rustdoc::broken-intra-doc-links` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(rustdoc::broken_intra_doc_links)]`

error: unresolved link to `flightsql`
   --> arrow-flight/src/sql/metadata/sql_info.rs:151:5

[alamb]

Example failure:

https://github.com/apache/arrow-rs/actions/runs/9807403342/job/27081102878?pr=6006

 Documenting arrow-flight v52.1.0 (/__w/arrow-rs/arrow-rs/arrow-flight)
error: unresolved link to `flightsql`
   --> arrow-flight/src/sql/metadata/sql_info.rs:137:61
    |
137 | /// Handles creating the dense [`UnionArray`] described by [flightsql]
    |                                                             ^^^^^^^^^ no item named `flightsql` in scope
    |
    = help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
    = note: `-D rustdoc::broken-intra-doc-links` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(rustdoc::broken_intra_doc_links)]`

error: unresolved link to `flightsql`
   --> arrow-flight/src/sql/metadata/sql_info.rs:151:5

[alamb]

label_issue.py automatically added labels {'arrow'} from #6012

[alamb]

label_issue.py automatically added labels {'arrow-flight'} from #6012

[alamb]

label_issue.py automatically added labels {'parquet'} from #6009