workflows: test on "push" not "pull_request".

This ensures they have access to the correct secrets.

.github/workflows/docker.yml

 name: Docker
 on:
-  pull_request:
+  push:
     paths:
       - .github/workflows/docker.yml
       - Dockerfile

.github/workflows/spdx.yml

 name: Update license data
 on:
-  pull_request:
+  push:
     paths:
       - .github/workflows/spdx.yml
   schedule: