update libwebp and libxml2

Author: henderkes

config/source.json

@@ -771,17 +771,20 @@
         ]
     },
     "libwebp": {
-        "type": "url",
-        "url": "https://github.com/webmproject/libwebp/archive/refs/tags/v1.3.2.tar.gz",
+        "type": "ghtagtar",
+        "repo": "webmproject/libwebp",
+        "match": "v1\\.\\d+\\.\\d+$",
         "provide-pre-built": true,
         "license": {
             "type": "file",
             "path": "COPYING"
         }
     },
     "libxml2": {
-        "type": "url",
-        "url": "https://github.com/GNOME/libxml2/archive/refs/tags/v2.12.5.tar.gz",
+        "type": "ghtagtar",
+        "repo": "GNOME/libxml2",
+        "match": "v2\\.\\d+\\.\\d+$",
+        "provide-pre-built": false,
         "license": {
             "type": "file",
             "path": "Copyright"