Update dependency httpcore to v0.18.0

Author: renovate[bot]

requirements-test.txt

@@ -13,7 +13,7 @@ grpclib==0.4.7 ; python_version >= "3.11" and python_version < "4.0"
 h11==0.14.0 ; python_version >= "3.11" and python_version < "4.0"
 h2==4.1.0 ; python_version >= "3.11" and python_version < "4.0"
 hpack==4.0.0 ; python_version >= "3.11" and python_version < "4.0"
-httpcore==0.16.3 ; python_version >= "3.11" and python_version < "4.0"
+httpcore==0.18.0 ; python_version >= "3.11" and python_version < "4.0"
 httpx==0.23.3 ; python_version >= "3.11" and python_version < "4.0"
 hyperframe==6.0.1 ; python_version >= "3.11" and python_version < "4.0"
 idna==3.8 ; python_version >= "3.11" and python_version < "4.0"