adapt callback integration test for HTTP v1

these didn't run since we updated our HTTP
dep back in `v1.2.0`

Author: etpinard

test/integration/callbacks/jl_callback_context/jlcbcx001_modified_response.jl

@@ -13,10 +13,11 @@ callback!(app,
 ) do value
     cookie = HTTP.Cookie("dash_cookie", value * " - cookie")
 
-    println(String(cookie, false))
+    cookie_str = HTTP.Cookies.stringify(cookie)
+    println(cookie_str)
     http_response = callback_context().response
-    push!(http_response.headers, "Set-Cookie"=>String(cookie, false))
+    push!(http_response.headers, "Set-Cookie"=>cookie_str)
     return value * " - output"
 end
 
-run_server(app)
+run_server(app)

test/integration/callbacks/test_callback_context.py

@@ -20,7 +20,7 @@ def test_jlcbcx001_modified_response(dashjl):
     dashjl.wait_for_text_to_equal("#output", "abcd - output")
     cookie = dashjl.driver.get_cookie("dash_cookie")
     # cookie gets json encoded
-    assert cookie["value"] == 'abcd - cookie'
+    assert cookie["value"] == '"abcd - cookie"'
 
     assert not dashjl.get_logs()
 
@@ -34,4 +34,4 @@ def test_jlcbcx002_triggered(dashjl):
             dashjl.find_element("#" + btn).click()
             dashjl.wait_for_text_to_equal(
                 "#output", "Just clicked {} for the {} time!".format(btn, i)
-            )
+            )