Fix license checks for non-go files

[mimir-d]

Issue by insomniacslk Thursday Dec 03, 2020 at 21:20 GMT Originally opened as https://github.com/facebookincubator/contest/issues/192

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As noted in https://github.com/facebookincubator/contest/pull/188 our CI doesn't detect correctly when non-go files are missing the copyright header. Specifically, despite adding *.sql to the configuration of checklicenses, it always reports success, even when the license header is missing or wrong.