meson build lists integration tests separately

[davmac314]

The meson.build file for the integration tests (src/igr-tests) contains a list of each test by name. This is problematic when new tests are added to the source (igr-runner) because the list goes out of sync and has to be manually updated. The build should be fixed so that it does not contain this list. It can be obtained by building igr-runner and requesting a list of test names (needs modification to igr-runner to support this), or by just running all tests as a whole via igr-runner.