[gimp] Makefile: update DISTCHECK_CONFIGURE_FLAGS to fix CI distcheck.

[Jehan <jehanp src gnome org>]

commit 6d2b6b8ea02e0b102a4304cf880fc373e96a406e
Author: Jehan <jehan girinstud io>
Date:   Mon Aug 3 18:17:48 2020 +0200

    Makefile: update DISTCHECK_CONFIGURE_FLAGS to fix CI distcheck.
    
    CI doesn't require various script interpreters to be present to
    generate the tarball.
    Also use AM_DISTCHECK_CONFIGURE_FLAGS because DISTCHECK_CONFIGURE_FLAGS
    is meant for users according to the docs.

 Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/Makefile.am b/Makefile.am
index 57c08a827b..d485a18b45 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -89,7 +89,7 @@ EXTRA_DIST = \
        gtk-doc.make
 
 
-DISTCHECK_CONFIGURE_FLAGS = --enable-gtk-doc
+AM_DISTCHECK_CONFIGURE_FLAGS = --enable-gtk-doc --with-python=force --with-javascript=force --with-lua=force
 
 
 check-defs: