ci: specify explicit dependencies between jobs

Use `needs` to specify job dependencies explicitly instead of relying on
stages for ordering. This allows jobs from multiple stages to run concurrently
without having to wait for unrelated jobs in earlier stages.

See https://docs.gitlab.com/ci/yaml/#needs for more information.

.gitlab-ci.yml

@@ -256,6 +256,9 @@ build_on_ubuntu:
     - .fdo.distribution-image@ubuntu
     - .build
   stage: build
+  needs:
+    - job: container_ubuntu
+      artifacts: false
   variables:
     MESON_OPTIONS: "-Dsession-managers=[] -Dsnap=enabled"
 
@@ -266,6 +269,9 @@ build_on_ubuntu:
     - .fdo.distribution-image@fedora
     - .build
   stage: build
+  needs:
+    - job: container_fedora
+      artifacts: false
 
 build_on_fedora:
   extends:
@@ -358,6 +364,9 @@ build_on_alpine:
     - .fdo.distribution-image@alpine
     - .build
   stage: build
+  needs:
+    - job: container_alpine
+      artifacts: false
   variables:
     MESON_OPTIONS: "-Dsession-managers=[] -Dsnap=disabled -Dlogind=enabled -Dlogind-provider=libelogind"
 
@@ -493,6 +502,9 @@ build_with_coverity:
     - .fdo.suffixed-image@fedora
     - .build
   stage: analysis
+  needs:
+    - job: container_coverity
+      artifacts: false
   script:
     - export PATH=/opt/coverity/bin:$PATH
     - meson setup "$BUILD_DIR" --prefix="$PREFIX"
@@ -568,8 +580,9 @@ check_missing_headers:
     - .not_coverity
     - .fdo.distribution-image@fedora
   stage: analysis
-  dependencies:
-    - build_on_fedora
+  needs:
+    - job: build_on_fedora
+      artifacts: true
   script:
     - export PREFIX=`find -name prefix-*`
     - ./.gitlab/ci/check_missing_headers.sh
@@ -578,8 +591,9 @@ pages:
   extends:
     - .not_coverity
   stage: pages
-  dependencies:
-    - build_on_fedora_html_docs
+  needs:
+    - job: build_on_fedora_html_docs
+      artifacts: true
   script:
     - mkdir public public/1.0 public/1.2 public/1.4 public/devel
     - cp -R branch-1.0/builddir/doc/html/* public/1.0/