main/doas: fix license

OpenDoas (and OpenBSD itself) are ISC licensed, not BSD licensed.

See:

* https://spdx.org/licenses/ISC.html
* https://github.com/Duncaen/OpenDoas/blob/master/LICENSE
7 jobs for !20200 with doas-license in 1 minute and 57 seconds
latest detached
Status Job ID Name Coverage
  Lint
passed #365372
docker-alpine x86_64
lint

00:00:24

 
  Build
passed #365377
docker-alpine ci-build aarch64
build-aarch64

00:00:55

passed #365378
docker-alpine ci-build armv7
build-armv7

00:00:46

passed #365376
docker-alpine ci-build ppc64le
build-ppc64le

00:01:00

passed #365375
docker-alpine ci-build s390x
build-s390x

00:01:09

passed #365374
docker-alpine ci-build x86
build-x86

00:00:26

passed #365373
docker-alpine ci-build x86_64
build-x86_64

00:00:28