Revert "Update Go module name" (#2)

This reverts commit 6668049.

If we leave the name alone replace will work properly in the
project's go.mod.  go get breaks when changing the pinned
version/commit but can be worked around by updating the
version in the replace line.

go.mod

@@ -1,4 +1,4 @@
-module github.com/saladtechnologies/oras-go
+module oras.land/oras-go/v2
 
 go 1.21