test(matrix): make the 502 SVG fixture actually embed "403"

The inherited fixture coordinate "40.4302" does not contain the substring
"403" (the dot splits it), so the old substring classifier also passed on
it and the case proved nothing. Use a coordinate that genuinely embeds the
digits so the test is red on the pre-fix classifier.

plugins/platforms/matrix/adapter.py

@@ -209,7 +209,7 @@ def _is_permanent_matrix_auth_error(exc: BaseException) -> bool:
     A transient homeserver outage surfaces as a 5xx whose body may be an HTML
     error page (Umbrel's app-proxy returns one). Naive substring checks like
     ``"403" in str(exc)`` false-positive on digits embedded in that HTML (an SVG
-    coordinate such as ``40.4302`` contains ``403``) or in the ``since`` token
+    path coordinate such as ``1403.2`` contains ``403``) or in the ``since`` token
     echoed by a timeout message, which stopped the sync loop permanently on a
     passing blip. mautrix raises ``MatrixRequestError`` with ``errcode`` and
     ``http_status`` for every non-2xx, so classify on those alone; anything