CI: add a github workflow that also builds on MacOS

Builds collocatordb, installs the perl dependencies and runs the tests on
ubuntu-latest and macos-latest. On MacOS with the perl of homebrew, so that the
modules can be installed without sudo and without running into the system
integrity protection.

Only test.t: server-test.t guesses the pids of the server it started and kills
them, which has no business on a machine it does not own.

The .gitignore ignores everything starting with a dot, so .github needs an
exception like .gitlab-ci.yml and .dockerignore have.

Verified on Linux by running the steps of the job as they are, which is how the
missing make install was found - the tests load the module from the perl
library path, not from the build directory. The MacOS job has not run yet, that
is what it is for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Change-Id: I9f70f080366f64053663bc4c9a36087aba2f9e4e
diff --git a/.gitignore b/.gitignore
index 1336b0e..8473980 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,4 @@
 **/LOG.old.*
 example-models/wpd19_10000/wpd19_10000.rocksdb/LOG
 !.dockerignore
+!.github/