Upgrade build system

.woodpecker/.build.yml

@@ -1,6 +1,8 @@
-pipeline:
-  run:
-    image: gradle:7.5-jdk8
+steps:
+  build:
+    when:
+      branch: main
+    image: gradle:8.8-jdk11
     commands:
       - git checkout $CI_COMMIT_BRANCH
       # Code works
@@ -9,4 +11,6 @@ pipeline:
       - gradle check javadocAll
       # Code has coverage
       - gradle jacocoRootReport coveralls
-    secrets: [COVERALLS_REPO_TOKEN]
+    environment:
+      COVERALLS_REPO_TOKEN:
+        from_secret: COVERALLS_REPO_TOKEN

.woodpecker/.reuse.yml

@@ -1,7 +1,9 @@
 # Code is licensed properly
 # See https://reuse.software/
-pipeline:
+steps:
   reuse:
+    when:
+      branch: main
     image: fsfe/reuse:latest
     commands:
       - reuse lint