。
It's not that I like both of them.
Literal
Both-together liked [quotative-という] [it's-not-the-case-that-わけではない].
という inserted before わけではない adds an explicit framing layer — 'it's not the case that one would say I like both.' This longer form of partial negation is slightly more deliberate and common in written or careful speech, leaving room for the nuance that the speaker may like one but not the other.