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 13 minutes and 12 seconds
Status Job ID Name Coverage
  Test
passed #244454203
codecov

00:08:51

99.76%
passed #244454201
test·jdk11

00:13:12

passed #244454202
test·jdk8

00:13:12