Split the ci_build_manifest in its own file

gitlab/ci_build_manifest.yml

+stages:
+  - "manifest"
+  - "build"
+
+variables:
+  GIT_STRATEGY: none
+
+manifest:
+  image: registry.freedesktop.org/thiblahute/gst-ci/amd64/alpine-manifest-build:latest
+  stage: "manifest"
+  script:
+    - cp -R /gst-ci . && cd gst-ci
+    - git fetch https://gitlab.freedesktop.org/thiblahute/gst-ci.git simple_manifest && git checkout FETCH_HEAD # REMOVEME!
+    - gitlab/build_manifest.py --self-update
+    - gitlab/build_manifest.py ${CI_PROJECT_DIR}/manifest.xml
+    - cat ${CI_PROJECT_DIR}/manifest.xml
+  artifacts:
+    expire_in: "2 days"
+    paths:
+      - manifest.xml
+      - gst-ci/
\ No newline at end of file

gitlab/ci_template.yml

-stages:
-  - "manifest"
-  - "build"
-
-variables:
-  GIT_STRATEGY: none
-
-manifest:
-  image: registry.freedesktop.org/thiblahute/gst-ci/amd64/alpine-manifest-build:latest
-  stage: "manifest"
-  script:
-    - cd /gst-ci
-    - git fetch https://gitlab.freedesktop.org/thiblahute/gst-ci.git simple_manifest && git checkout FETCH_HEAD # REMOVEME!
-    - gitlab/build_manifest.py --self-update
-    - gitlab/build_manifest.py ${CI_PROJECT_DIR}/manifest.xml
-    - cat ${CI_PROJECT_DIR}/manifest.xml
-  artifacts:
-    expire_in: "2 days"
-    paths:
-      - "manifest.xml"
-
 .build:
   stage: "build"
   dependencies: