gtk-doc: Fix potential shebang overflow on gtkdoc-mkhtml2

A native path can cause a shebang overflow on gtkdoc-mkhtml.
Replace it with /usr/bin/env.

(From OE-Core rev: f018d3f77f27b73206a26c78228fed563950bd9d)

Signed-off-by: Paulo Neves <ptsneves@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-gnome/gtk-doc/gtk-doc_1.33.2.bb

@@ -43,6 +43,7 @@ do_install:append () {
         ${datadir}/gtk-doc/python/gtkdoc/config.py; do
         sed -e 's,${RECIPE_SYSROOT_NATIVE}/usr/bin/pkg-config,${bindir}/pkg-config,' \
             -e 's,${HOSTTOOLS_DIR}/python3,${bindir}/python3,' \
+            -e '1s|^#!.*|#!/usr/bin/env python3|' \
             -i ${D}$fn
     done
 }