tests: install: Fix timezone check.

The default timezone is set to Europe/Zaghreb, however the new check
introduced in 0a9eb3f3e2 was checking for the
one in the operating-system definition, which is Europe/Paris.

* gnu/tests/install.scm (gui-test-program): Explicitely set timezone to
Europe/Paris.

Change-Id: I7b5d327f13760632c9fbc0c1223a6a9bbc624f4d
Signed-off-by: Rutherther <rutherther@ditigal.xyz>
Merges: #4977

gnu/tests/install.scm

@@ -1901,7 +1901,9 @@ build (current-guix) and then store a couple of full system images.")
                         #$marionette)
       (screenshot "installer-start.ppm")
 
-      (marionette-eval* '(choose-locale+keyboard installer-socket)
+      (marionette-eval* '(choose-locale+keyboard
+                          installer-socket
+                          #:timezone '("Europe" "Paris"))
                         #$marionette)
       (screenshot "installer-locale.ppm")