pg_regress: Disable autoruns for cmd.exe on Windows

This is similar to 9886744a36, to prevent the execution of other
programs due to autorun configurations which could influence the
postmaster startup.

Like the other change, no backpatch is done.

Discussion: https://postgr.es/m/20230922.161551.320043332510268554.horikyota.ntt@gmail.com

src/test/regress/pg_regress.c

@@ -1242,7 +1242,7 @@ spawn_process(const char *cmdline)
 		comspec = "CMD";
 
 	memset(&pi, 0, sizeof(pi));
-	cmdline2 = psprintf("\"%s\" /c \"%s\"", comspec, cmdline);
+	cmdline2 = psprintf("\"%s\" /d /c \"%s\"", comspec, cmdline);
 
 	if (!CreateRestrictedProcess(cmdline2, &pi))
 		exit(2);