Build: Fix libpxbackend dependency mismatch

libpxbackend was not being installed from vcpkg which lead to use of
libpxbackend on the system causing library mismatch in rolling
distros(ie arch linux)

a

vcpkg.json

@@ -57,6 +57,7 @@
         "apng"
       ]
     },
+    "libproxy",
     {
       "name": "libavif",
       "features": [
@@ -145,6 +146,10 @@
       "name": "libpng",
       "version": "1.6.43#3"
     },
+    {
+      "name": "libproxy",
+      "version": "0.4.18#3"
+    },
     {
       "name": "libavif",
       "version": "1.0.4#1"