GRADLE_PUBLISH_KEY and GRADLE_PUBLISH_SECRET are not available to publish_gradle_plugin

[wilkinsona]

I think the keys need to be changed to upper-case in the pipeline:

spring-boot/ci/pipeline.yml

Lines 89 to 90 in aa216dd

	gradle_publish_key: ((gradle-publish-key))
	gradle_publish_secret: ((gradle-publish-secret))