.gitlab-ci.yml: Bump version of fd.o SDK and bst_external in overnight tests

.gitlab-ci.yml

@@ -182,8 +182,8 @@ docs:
   stage: test
   variables:
     BST_EXT_URL: git+https://gitlab.com/BuildStream/bst-external.git
-    BST_EXT_REF: 1d6ab71151b93c8cbc0a91a36ffe9270f3b835f1 # 0.5.1
-    FD_SDK_REF: 88d7c22c2281b987faa02edd57df80d430eecf1f # 18.08.11-35-g88d7c22c
+    BST_EXT_REF: 8a97ee76a5d51a150ae44dfefcc59d1960268626 # valentindavid/merge_git_and_git_tag merged
+    FD_SDK_REF: 612f66e218445eee2b1a9d7dd27c9caba571612e # freedesktop-sdk-18.08.19-54-g612f66e2
   before_script:
   - |
     mkdir -p "${HOME}/.config"