Fix `make test`

[cadmiumcat]

What

We no longer use travis for PR testing, so we can't rely on .travis being there. Instead look for the list of tasks on the github workflow and run make for each of them

How to review

Run make test and check it works as expected

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[AP-Hunt]

A more Make-idiomatic way to do this, I think, is to have it depend on the tasks by expanding a variable:

TEST_TARGETS := $(shell cat .github/workflows/test_on_pr.yml  | ruby -ryaml -e 'puts YAML.load(STDIN.read)["jobs"]["tests"]["strategy"]["matrix"]["make_task"].map { |j| puts j}')
.PHONY: test
test: $(TEST_TARGETS)# Run the same tests that run on a PR

Has the upside of not double invoking Make, which will make it easier to debug if we need to.