Block doc comment without continuing asterisk (`*`) doesn't align asterisk in starter/closer

Summary

I tried to format this code:

https://github.com/rust-lang/rustfmt/blob/2d897e21c73042bbea04640fe21077660367e29f/tests/target/6639-non-idempotent-block-doc-comments/outer-block-doc-comment.rs#L5-L7

Expected behavior

I expected to see this happen:

I'm unsure about ideal formatting, but maybe the asterisk (*) of the block doc comment starter/closer should align? Maybe

/**
foo
 */
mod foo;

Rationale is that in fixing a related non-idempotent closer rewrite (https://github.com/rust-lang/rustfmt/pull/7017), the fix changes block doc formatting to align the starter/closer by asterisk when there is a continuing (*):

/**
 * foo
 */
mod foo;

This matches block doc comment formatting I've seen in other languages (e.g. javadoc). See discussion.

Actual behavior

Instead, this happened: no formatting changes; this is the stable formatting.

Configuration

rustfmt cli options used (if applicable): none needed

rustfmt configuration file (e.g. rustfmt.toml, if applicable): N/A

Reproduction Steps

Just plain rustfmt will do.

Meta

rustfmt --version:

rustfmt 1.9.0-stable (48a229ceae 2026-09-01)

Start with tests/target/6639-non-idempotent-block-doc-comments/outer-block-doc-comment.rs and run plain rustfmt to reproduce the current stable output. Review the related rustfmt PR 7017 discussion for context, then confirm the intended starter/closer alignment for a block doc comment without continuing asterisks; done means the behavior is formatted consistently and remains stable on repeated runs.