internal/postgres: replace LegacyPackage in insert_module_test.go
internal/postgres: replace LegacyPackage in insert_module_test.go

For golang/go#39629

Change-Id: I8b2f8eda2035ad121abd01922f1938f9e0db5caa
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/263202
Trust: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite