*: git.monogon.dev -> source.monogon.dev

This implements T882, setting our (virtual) GOPATH to source.monogon.dev
for this repository.

Test Plan: Refactor, CI only.

X-Origin-Diff: phab/D686
GitOrigin-RevId: c5e2309089948ffc3a98e68e2e0e1cbb157d3a36
diff --git a/BUILD b/BUILD
index df5db5b..043c474 100644
--- a/BUILD
+++ b/BUILD
@@ -2,7 +2,7 @@
 load("//build/fietsje:def.bzl", "fietsje")
 load("@io_bazel_rules_go//go:def.bzl", "go_path", "nogo")
 
-# gazelle:prefix git.monogon.dev/source/nexantic.git
+# gazelle:prefix source.monogon.dev
 gazelle(name = "gazelle")
 
 fietsje(name = "fietsje")