ci/cd: work around GitLab Runner issue with caching

Signed-off-by: 35V LG84 <35vlg84-x4e6b92@e257.fi>
3 jobs for wip/scala-2.13 in 14 minutes and 29 seconds
Status Job ID Name Coverage
  Test
passed #242425278
codecov

00:10:02

99.76%
passed #242425276
test·jdk11

00:14:29

passed #242425277
test·jdk8

00:13:15