Fix my cmake vandalization for ESI unit test

[ywkaras]

I made this cringy change to get the unit test executable to link without unresolved symbol errors: https://github.com/apache/trafficserver/pull/10390/files#diff-9a7d501ccbcc5dedf3bd3cf04c034dd8479249a4ff24a09b3c347178f2cd558b

Maybe somebody who isn't cmake-impaired knows a better way to get this to work.