Use string concatenation for prepending base URL for log_url (#33063)

It is observed that urljoin is not yielding expected results for
the task instance's log_url which needs to be a concatenation of the
webserver base_url and specified relative url. The current usage
of urljoin does not seem to be the right way to achieve this based
on what urljoin is meant for and how it works. So, we use simple
string concatenation to yield the desired result.
More context in the comment apache/airflow#31833 (comment)

closes: #32996
(cherry picked from commit baa1bc0438baa05d358b236eec3c343438d8d53c)
GitOrigin-RevId: 868d1389461822cf5d54faaff3ce19913fc7f08e

airflow/models/taskinstance.py

@@ -33,7 +33,7 @@
 from pathlib import PurePath
 from types import TracebackType
 from typing import TYPE_CHECKING, Any, Callable, Collection, Generator, Iterable, Tuple
-from urllib.parse import quote, urljoin
+from urllib.parse import quote
 
 import dill
 import jinja2
@@ -779,26 +779,28 @@ def log_url(self) -> str:
         """Log URL for TaskInstance."""
         iso = quote(self.execution_date.isoformat())
         base_url = conf.get_mandatory_value("webserver", "BASE_URL")
-        return urljoin(
-            base_url,
-            f"log?execution_date={iso}"
+        return (
+            f"{base_url}"
+            "/log"
+            f"?execution_date={iso}"
             f"&task_id={self.task_id}"
             f"&dag_id={self.dag_id}"
-            f"&map_index={self.map_index}",
+            f"&map_index={self.map_index}"
         )
 
     @property
     def mark_success_url(self) -> str:
         """URL to mark TI success."""
         base_url = conf.get_mandatory_value("webserver", "BASE_URL")
-        return urljoin(
-            base_url,
-            f"confirm?task_id={self.task_id}"
+        return (
+            f"{base_url}"
+            "/confirm"
+            f"?task_id={self.task_id}"
             f"&dag_id={self.dag_id}"
             f"&dag_run_id={quote(self.run_id)}"
             "&upstream=false"
             "&downstream=false"
-            "&state=success",
+            "&state=success"
         )
 
     @provide_session