CI: don't needlessly run tests twice

Verifying that forth.bin is stable is enough. Also, fix shebang.

runtests.sh

@@ -1,4 +1,4 @@
-#/bin/sh -e
+#!/bin/sh -e
 
 git submodule init
 git submodule update
@@ -7,6 +7,8 @@ git clean -fxd
 make -C emul
 make -C tests
 
-# let's try again with an updated boot bin
-make -C emul updatebootstrap all
-make -C tests
+# verify that forth.bin is stable
+cp emul/forth.bin ref.bin
+make -C emul updatebootstrap
+cmp emul/forth.bin ref.bin
+rm ref.bin