ci: run tests with race detector

[fho]

ci: enable the race detector when running go tests

Pass "-race" when running the tests via the Makefile or in CI.
This enables the race detector and can catch some bugs.

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make: define all targets as phony

This prevents that Make skips running a target if a file with the same
name then target exist.

[fho]

@lukebakken I now realized that project also has a github actions config which is used.
So "-race" also needs to be added when running tests via github actions.

Is travis CI also used somehow? Or could the config be removed?

[lukebakken]

Oh, good catch. I forgot we're not using the make target for GitHub actions.

Yes, please feel free to remove the .travis.yml file.