Use upstream libxml2 repository

The incompatibilities have been fixed upstream.

Author: arichardson

pycheribuild/projects/cross/qt5.py

@@ -1018,7 +1018,9 @@ def process(self):
 
 # it also needs libxml2
 class BuildLibXml2(CrossCompileCMakeProject):
-    repository = GitRepository("https://github.com/CTSRD-CHERI/libxml2")
+    repository = GitRepository(
+        "https://gitlab.gnome.org/GNOME/libxml2.git", old_urls=[b"https://github.com/CTSRD-CHERI/libxml2"]
+    )
     native_install_dir = DefaultInstallDir.BOOTSTRAP_TOOLS
     supported_architectures = CompilationTargets.ALL_FREEBSD_AND_CHERIBSD_TARGETS + CompilationTargets.ALL_NATIVE