Use local modulesets.

This will allow local changes to take effect, which is useful for:
- contributors check out the repo, make fixes and test locally
- running in a GitHub workflow before committing to master

jhbuildrc-custom

@@ -6,5 +6,6 @@ build_policy = "updated-deps"
 modules = ["python3", "meta-osx-xpra-deps"]
 
 #change moduleset
-moduleset="https://raw.githubusercontent.com/Xpra-org/gtk-osx-build/master/xpra-gtk3.modules"
+moduleset="xpra-gtk3.modules"
+modulesets_dir = "."
 #os.environ["SSL_CERT_FILE"] = "/Users/osx/gtk/inst/etc/ssl/cacert.pem"

xpra-gtk3.modules

@@ -5,7 +5,7 @@
 
 	<repository type="tarball" name="xpra.org" default="yes" href="https://xpra.org"/>
 
-	<include href="https://raw.githubusercontent.com/Xpra-org/gtk-osx-build/master/modulesets-stable/gtk-osx.modules"/>
+	<include href="modulesets-stable/gtk-osx.modules"/>
 	<include href="xpra-tools.modules"/>
 	<include href="xpra-codecs.modules"/>
 	<include href="xpra-python3.modules"/>