.gitignore: add some entries

All either generated by the build system or some "standard tools".
3 jobs for gitignore-update in 1 minute and 6 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #3117
docker linux amd64
build:linux:amd64

00:00:30

 
  Test
passed #3119
docker linux amd64
deckard:linux:amd64

00:00:35

passed #3118
docker linux amd64
test:linux:amd64

00:00:31