coverage: adapt to Ansible lookup('dict') idiosyncrasy

That thing returns a list, unless the dict has a single item, in which
case it fails. WAT.

Change-Id: I9f92aaaceccd2b8460a1c2a427c8d95a371ed767
diff --git a/roles/git-use-previous-commit/tasks/main.yaml b/roles/git-use-previous-commit/tasks/main.yaml
index 9c371e9..cb7458e 100644
--- a/roles/git-use-previous-commit/tasks/main.yaml
+++ b/roles/git-use-previous-commit/tasks/main.yaml
@@ -4,4 +4,4 @@
     git checkout -b "zuul_origin_{{ zuul.branch }}" "origin/{{ zuul.branch }}"
   args:
     chdir: "{{ ansible_user_dir }}/{{ item.value.src_dir }}"
-  loop: "{{ lookup('dict', zuul.projects) }}"
+  loop: "{{ query('dict', zuul.projects) }}"