Add version to tikv-jemallocator git dependency to fix docs CI

[ndr-ds]

Motivation

The test-crates-and-docrs CI job has been failing on testnet_conway since the
backport of #5602 (#5792). cargo package requires all dependencies to have a version
field — the backport included the git spec but dropped version = "0.6".

Proposal

Add version = "0.6" to the tikv-jemallocator workspace dependency, matching what
#5602 has on main. The [patch.crates-io] section still ensures the git fork is used
at build time; the version is only needed so cargo package knows what to reference
when
stripping git specs for packaging.

Also temporarily adds a pull_request trigger to the Documentation workflow so the fix
can be verified on this PR before merging. This trigger should be removed before or
after merge.

Test Plan

• CI — the test-crates-and-docrs job will run on this PR via the temporary trigger

[ndr-ds]

Merging since this partially breaks the docs tests