ci: ensure containers run on amd64

.woodpecker/containers-packaging.yaml

@@ -4,6 +4,9 @@ when:
   path:
     include: ["docker/packaging/**/*", ".woodpecker/containers-packaging.yaml"]
 
+labels:
+  platform: linux/amd64
+
 matrix:
   PACKAGING_IMAGE:
     - archlinux

.woodpecker/containers-prod.yaml

@@ -2,6 +2,9 @@ when:
   event: [ push ]
   branch: master
 
+labels:
+  platform: linux/amd64
+
 matrix:
   PROD_IMAGE:
     - alpine

.woodpecker/containers-test.yaml

@@ -4,6 +4,9 @@ when:
   path:
     include: ["docker/test/**/*", ".woodpecker/containers-test.yaml"]
 
+labels:
+  platform: linux/amd64
+
 matrix:
   TEST_IMAGE:
     - alpine

.woodpecker/docs.yaml

@@ -4,6 +4,9 @@ when:
     include: ["CMakeLists.txt", ".woodpecker/docs.yaml", "doc/**/*"]
   event: [pull_request, push]
 
+labels:
+  platform: linux/amd64
+
 clone:
   - name: git
     image: woodpeckerci/plugin-git