Add "latex-dev" do docs for known formats

l3build.dtx

@@ -433,7 +433,7 @@
 % configurations are used and need adjustment to the standard engine, this does
 % need to be given explicitly using \var{stdengine}.
 % The format used for tests can be altered by setting \var{checkformat}: the default setting \texttt{latex} means that tests are run using \emph{e.g.}~\texttt{pdflatex}, whereas setting to \texttt{tex} will run tests using \emph{e.g.}~\texttt{pdftex}.
-% (Currently, this should be one of \texttt{latex}, \texttt{tex}, or
+% (Currently, this should be one of \texttt{latex}, \texttt{latex-dev}, \texttt{tex}, or
 % \texttt{context}.)
 % To perform the check, the engine typesets each test up to \var{checkruns} times.
 % More detail on this in the documentation on |save|.