build: add new Belarusian translation in the installer.

This localization was added recently but it was not in the installer scripts.
Discovered with unit testing: meson test gimp:build / windows-installer-langs

build/windows/gitlab-ci/installer-gimp-msys2.sh

@@ -46,6 +46,7 @@ add_bom ()
 
 
 download_lang Basque.isl
+download_lang Belarusian.isl
 download_lang ChineseSimplified.isl
 download_lang ChineseTraditional.isl
 # Supposed to be UTF-8 yet missing BOM.

build/windows/installer/gimp3264.iss

@@ -187,6 +187,7 @@ PrivilegesRequiredOverridesAllowed=dialog
 
 [Languages]
 Name: "en"; MessagesFile: "compiler:Default.isl,lang\en.setup.isl"
+Name: "be"; MessagesFile: "compiler:Languages\Unofficial\Belarusian.isl,lang\be.setup.isl"
 Name: "bg"; MessagesFile: "compiler:Languages\Bulgarian.isl,lang\bg.setup.isl"
 Name: "ca"; MessagesFile: "compiler:Languages\Catalan.isl,lang\ca.setup.isl"
 Name: "cs"; MessagesFile: "compiler:Languages\Czech.isl,lang\cs.setup.isl"

build/windows/installer/lang/meson.build

@@ -8,6 +8,7 @@ ms_installer_config_xml = i18n.merge_file(
 )
 
 languages = [
+  { 'code': 'be',    },
   { 'code': 'bg',    },
   { 'code': 'ca',    },
   { 'code': 'cs',    },