test: reproduce syntax error as in ocaml#4230

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

Author: rgrinberg

test/blackbox-tests/test-cases/gh4230.t

@@ -0,0 +1,15 @@
+Syntax error inside a cram command
+  $ mkdir foo && cd foo
+  $ cat >dune-project <<EOF
+  > (lang dune 3.0)
+  > EOF
+
+  $ cat >t1.t <<EOF
+  >   $ foo-bar() { true; }
+  > EOF
+
+  $ dune runtest --auto-promote
+            sh (internal) (exit 2)
+  (cd _build/.sandbox/cdb38568b2ab5eaeeab253debbcff1a1/default && /run/current-system/sw/bin/sh /var/folders/nc/x9_nmmsj0rjbfyzxb_kjk6qr0000gn/T/build_75e3fc_dune/dune_cram_b748db_.t1.t/main.sh)
+  -> required by alias runtest
+  [1]