main/etckeeper: upgrade to 1.18.15

upstream is no longer shipping the cron job
7 jobs for !14915 with etckeeper-1.18.15 in 51 seconds
detached
Status Job ID Name Coverage
  Lint
passed #254188
docker-alpine x86_64
lint

00:00:25

 
  Build
failed #254193
docker-alpine ci-build aarch64
build-aarch64

00:00:07

failed #254194
docker-alpine ci-build armv7
build-armv7

00:00:12

failed #254192
docker-alpine ci-build ppc64le
build-ppc64le

00:00:11

failed #254191
docker-alpine ci-build s390x
build-s390x

00:00:11

failed #254190
docker-alpine ci-build x86
build-x86

00:00:07

failed #254189
docker-alpine ci-build x86_64
build-x86_64

00:00:09

 
Name Stage Failure
failed
build-ppc64le Build
No job log
failed
build-aarch64 Build
No job log
failed
build-x86 Build
No job log
failed
build-armv7 Build
No job log
failed
build-s390x Build
No job log
failed
build-x86_64 Build
No job log