test(io): fix freeport function to prevent failures

Sometimes, a healthcheck related test fails as occurred in
https://github.com/PostgREST/postgrest/actions/runs/19771357953/job/56655949002.
This happens due to freeport function accidently picking up a used port.

Signed-off-by: Taimoor Zaeem <taimoorzaeem@gmail.com>
(cherry picked from commit 50eec773bf)

test/io/postgrest.py

@@ -113,7 +113,7 @@ def run(
             env["PGRST_SERVER_UNIX_SOCKET"] = str(socketfile)
             baseurl = "http+unix://" + urllib.parse.quote_plus(str(socketfile))
 
-        adminport = freeport(port)
+        adminport = freeport(used_ports=[port])
         env["PGRST_ADMIN_SERVER_PORT"] = str(adminport)
         adminhost = f"[{host}]" if host and is_ipv6(host) else localhost
         adminurl = f"http://{adminhost}:{adminport}"
@@ -165,14 +165,14 @@ def run(
                 process.wait()
 
 
-def freeport(used_port=None):
-    "Find a free port on localhost."
+def freeport(used_ports=None):
+    "Find an unused free port on localhost."
     while True:
         with contextlib.closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
             s.bind(("", 0))
             s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
             port = s.getsockname()[1]
-            if port != used_port:
+            if used_ports is None or port not in used_ports:
                 return port