[gimp] gitlab-ci: install GIMP before running `make check`.

[Jehan <jehanp src gnome org>]

commit fe329adcf5f0f6837f5e741f383cf8db511a6a54
Author: Jehan <jehan girinstud io>
Date:   Tue Jul 6 15:54:37 2021 +0200

    gitlab-ci: install GIMP before running `make check`.
    
    Since GIMP looks for its icons at runtime and would output warnings if
    it doesn't find them, it's better to install first. Not really sure it's
    ideal though, but it will do for now. Maybe I should just g_printerr()
    instead of g_warning().

 .gitlab-ci.yml | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index d82f83c87d..47d137f822 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -213,6 +213,7 @@ gimp-distcheck-debian:
         --enable-gtk-doc
         --enable-windows-installer
     - make -j "$(nproc)"
+    - make -j "$(nproc)" install
     - make -j "$(nproc)" check
     - make -j "$(nproc)" distcheck