doc: bump ICU version to avoid confusion

ICU has been on 6X for a while but example file name in Intl docs
still refers to it as 5X. It might be a small thing but I think
it's good to update this to avoid confusion.

PR-URL: nodejs#22313
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: George Adams <george.adams@uk.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/intl.md

@@ -133,7 +133,7 @@ through either:
 
 ICU is able to automatically find and load a variety of data formats, but the
 data must be appropriate for the ICU version, and the file correctly named.
-The most common name for the data file is `icudt5X[bl].dat`, where `5X` denotes
+The most common name for the data file is `icudt6X[bl].dat`, where `6X` denotes
 the intended ICU version, and `b` or `l` indicates the system's endianness.
 Check ["ICU Data"][] article in the ICU User Guide for other supported formats
 and more details on ICU data in general.