[gimp/wip/Jehan/master-distcheck] gitlab-ci: add a distcheck step on master too.

[Jehan <jehanp src gnome org>]

commit 78fe9776368cb4e077b4d9c23d420d77cce98a6f
Author: Jehan <jehan girinstud io>
Date:   Mon Aug 3 02:27:29 2020 +0200

    gitlab-ci: add a distcheck step on master too.
    
    Similar to the distcheck step only contributed by schumaml on gimp-2-10.

 .gitlab-ci.yml | 13 +++++++++++++
 1 file changed, 13 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 4036a3dca0..c8fad5629c 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -144,6 +144,19 @@ gimp-debian/testing-autotools:
     - make -j "$(nproc)"
     - make check
 
+gimp-debian/testing-autotools-distcheck:
+  extends: .gimp-debian/testing-base
+  script:
+    - mkdir _build
+    - cd _build
+    - ../autogen.sh
+        --prefix="${INSTALL_PREFIX}"
+        --enable-debug
+        --enable-gtk-doc
+    - make -j "$(nproc)"
+    - make distcheck
+  allow_failure: true
+
 gimp-debian/testing-meson:
   extends: .gimp-debian/testing-base
   script: