CI: switch to gitlab

.builds/build.yml

-image: alpine/edge
-packages:
-  - curl-dev
-  - build-base
-sources:
-  - https://git.roshless.me/~roshless/fup
-artifacts:
-  - "fup/fup"
-tasks:
-  - build: |
-      cd fup
-      make all

.gitlab-ci.yml

+build-artifact:
+  image: alpine:3.15
+  stage: build
+  artifacts:
+    paths:
+      - fup/fup
+    expire_in: 32 weeks
+  before_script:
+    - apk add build-base curl-dev git
+  script:
+    - git clone https://git.roshless.me/roshless/fup fup
+    - cd fup
+    - make all
+