doc: move --stderr-prefix doc details to a new subsubsection.

Still in https://bugs.gnu.org/72536.

* doc/automake.texi (TAP setup and examples):
(TAP stderr examples),
TAP stderr prefixing): split TAP examples
into new subsubsections. Add discussion of race condition and
other reordering from the open bug.
* NEWS: mention --stderr-prefix.
2 files changed