fix: add missing mocks

Signed-off-by: Norman Stetter <85173861+norman-zon@users.noreply.github.com>

Author: norman-zon

internal/gatewayapi/luavalidator/mocks.lua

@@ -587,6 +587,10 @@ function StreamHandle:connectionStreamInfo()
   return ConnectionStreamInfo
 end
 
+function StreamHandle:filterContext()
+  return {key = "value"}
+end
+
 function StreamHandle:setUpstreamOverrideHost(host, strict)
 end