gitlab-ci, build: BUILD_TYPE not set for packaging-win-a64 job.

Aaaargh! I think this was the main issue which would explain why the problem was
mostly happening on the packaging job. In this job, we were still consistently
calling `pacman --noconfirm -Suy` (i.e.g "Synchronizing package databases")
which we had stopped to do for the CI builds as that was highly increasing
chances of locking pacman's process.

.gitlab-ci.yml

@@ -753,6 +753,7 @@ packaging-win-a64:
     - if: '$CI_MERGE_REQUEST_LABELS =~ /.*5. Windows Installer.*/'
   stage: packaging
   variables:
+    BUILD_TYPE: "CI_NATIVE"
     MSYSTEM: "CLANGARM64"
     CHERE_INVOKING: "yes"
   tags:

build/windows/gitlab-ci/3_package-gimp-uni_base.sh

@@ -19,7 +19,7 @@ else # [[ "$CROSSROAD_PLATFORM" == "w32" ]] || [[ "$MSYSTEM_CARCH" == "i686" ]];
 fi
 
 if [[ "$BUILD_TYPE" != "CI_CROSS" ]] && [[ "$BUILD_TYPE" != "CI_NATIVE" ]]; then
-pacman --noconfirm -Suy
+  pacman --noconfirm -Suy
 fi