Fix log text selection contrast in light mode (apache#56216)

* Fix log text selection contrast in light mode

  Changed selection background from brand.subtle to gray.emphasized
  to improve readability when highlighting text in the log viewer.
  This aligns with the DAG code viewer styling and provides better
  contrast across both light and dark themes.

* Brent's suggestions

Author: dheerajturaga

airflow-core/src/airflow/ui/src/pages/TaskInstance/Logs/TaskLogContent.tsx

@@ -114,11 +114,6 @@ export const TaskLogContent = ({ error, isLoading, logError, parsedLogs, wrap }:
       <ErrorAlert error={error ?? logError} />
       <ProgressBar size="xs" visibility={isLoading ? "visible" : "hidden"} />
       <Code
-        css={{
-          "& *::selection": {
-            bg: "brand.subtle",
-          },
-        }}
         data-testid="virtualized-list"
         flexGrow={1}
         h="auto"