Fix headers handling for Julia 1.10 compatibility

Use union! with append! on headers.entries instead of push! or append!
directly on headers. This works consistently across Julia 1.10 and 1.12
where the push! behavior differs.

Author: hhaensel

src/Renderer.jl

@@ -294,7 +294,7 @@ function respond(r::WebRenderable) :: HTTP.Response
   if haskey(Genie.Router.params(), Genie.Router.PARAMS_RESPONSE_KEY)
     params_resp = Genie.Router.params(Genie.Router.PARAMS_RESPONSE_KEY)
     # Merge headers from params response (e.g., Set-Cookie from sessions)
-    append!(r.headers, params_resp.headers)
+    union!(append!(r.headers.entries, HTTP.mkheaders(params_resp.headers)))
   end
 
   HTTP.Response(r.status, r.headers, body = r.body)

src/Responses.jl

@@ -23,19 +23,16 @@ function getheaders() :: HTTP.Headers
 end
 
 
-function setheaders!(res::HTTP.Response, headers::Dict) :: HTTP.Response
-  push!(res.headers, [headers...]...)
+function setheaders!(res::HTTP.Response, headers) :: HTTP.Response
+  union!(append!(res.headers.entries, HTTP.mkheaders(headers)))
 
   res
 end
-function setheaders(headers::Dict) :: HTTP.Response
+function setheaders(headers) :: HTTP.Response
   setheaders!(getresponse(), headers)
 end
 function setheaders(header::Pair{String,String}) :: HTTP.Response
-  setheaders(Dict(header))
-end
-function setheaders(headers::Vector{Pair{String,String}}) :: HTTP.Response
-  setheaders(Dict(headers...))
+  setheaders([header])
 end