Does Galatians 1:7-9 refer to the Gnostic Gospels?
No, not technically. The Gnostic Gospels were written at least a century later.
Although the manuscripts [Gnostic Gospels] discovered at Nag Hammadi are generally dated to the 4th century, there is some debate regarding the original composition of the texts.
The Gospel of Thomas is held by most to be the earliest of the "gnostic" gospels composed. Scholars generally date the text to the early-mid 2nd century.
Prophetically, Galatians 1:7-9 could refer to the Gnostic Gospels.