ci/build-generic.yaml: Force pulling LFS blobs

Since https://gerrit-review.googlesource.com/c/git-repo/+/83130/

 repo
requires manual handling of LFS blobs.

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

.oniro-ci/build-generic.yaml

@@ -295,6 +295,7 @@
     name: registry.booting.oniroproject.org/distro/oniro/docs-builder:latest
   stage: build
   script:
+    - (cd docs && git lfs pull)
     - make -C docs
   artifacts:
     paths: