Fix TestHttp.test_html_internet on Python 3.12.6

A relative path in a URL without netloc is preserved in
urllib.parse.urlunsplit().

https://docs.python.org/3.12/whatsnew/changelog.html#id4

tests/checker/data/http_slash-old-urlunsplit.html

@@ -0,0 +1,7 @@
+<a href="http://www.example.com/">ok example</a>
+<a href="http:/www.example.com/">one slash example</a>
+<a href="http:www.example.com/">no slash example</a>
+<a href="//www.example.com/">no scheme example</a>
+<a href="http://">no url</a>
+<a href="http:/">no url, one slash</a>
+<a href="http:">no url, no slash</a>

tests/checker/data/http_slash-old-urlunsplit.html.result

@@ -0,0 +1,40 @@
+url http://localhost:%(port)d/%(datadir)s/http_slash-old-urlunsplit.html
+cache key http://localhost:%(port)d/%(datadir)s/http_slash-old-urlunsplit.html
+real url http://localhost:%(port)d/%(datadir)s/http_slash-old-urlunsplit.html
+valid
+
+url http:
+cache key None
+real url http://
+name no url, no slash
+error
+
+url http:/
+cache key None
+real url http:///
+name no url, one slash
+error
+
+url http://
+cache key None
+real url http://
+name no url
+error
+
+url http:www.example.com/
+cache key None
+real url http:///www.example.com/
+name no slash example
+error
+
+url http:/www.example.com/
+cache key None
+real url http:///www.example.com/
+name one slash example
+error
+
+url http://www.example.com/
+cache key http://www.example.com/
+real url http://www.example.com/
+name ok example
+valid

tests/checker/data/http_slash.html.result

@@ -23,7 +23,7 @@ error
 
 url http:www.example.com/
 cache key None
-real url http:///www.example.com/
+real url http:www.example.com/
 name no slash example
 error
 

tests/checker/test_http.py

@@ -16,6 +16,7 @@
 """
 Test http checking.
 """
+import sys
 
 from tests import need_network
 from .httpserver import HttpServerTest, CookieRedirectHttpRequestHandler
@@ -34,7 +35,11 @@ class TestHttp(HttpServerTest):
         self.file_test("http.html", confargs=confargs)
         self.file_test("http_lowercase.html", confargs=confargs)
         self.file_test("http_quotes.html", confargs=confargs)
-        self.file_test("http_slash.html", confargs=confargs)
+        if sys.version_info < (3, 12, 6):
+            http_slash_html = "http_slash-old-urlunsplit.html"
+        else:
+            http_slash_html = "http_slash.html"
+        self.file_test(http_slash_html, confargs=confargs)
         self.file_test("http_url_quote.html", confargs=confargs)
 
     def test_html(self):