📌(backend) pin lxml dependency to 5.2.1

With the constraint on lxml<5, an error on the collectstatic occured about lxml
and xmlsec libxml2 versions mismatch. Pin lxml to the latest release fix this
error.

renovate.json

@@ -59,16 +59,6 @@
       ],
       "allowedVersions": "<5"
     },
-    {
-      "groupName": "allowed lxml versions",
-      "matchManagers": [
-        "setup-cfg"
-      ],
-      "matchPackageNames": [
-        "lxml"
-      ],
-      "allowedVersions": "<5"
-    },
     {
       "groupName": "allowed pytest versions",
       "matchManagers": [

src/backend/setup.cfg

@@ -54,7 +54,7 @@ install_requires =
     drf-spectacular==0.27.1
     gunicorn==21.2.0
     logging-ldp==0.0.7
-    lxml<5
+    lxml==5.2.1
     oauthlib==3.2.2
     Pillow==10.2.0
     psycopg[binary]==3.1.18