Fix broken short date test with ICU >= 72.1 (#8904)

• tests/Rcmail/Rcmail.php (test_format_date): Starting with ICU 72.1,

a NARROW NO-BREAK SPACE (NNBSP) is used instead of an ASCII space
before the meridian. So, check for an NNBSP when using ICU >= 72.1.

References:

• https://icu.unicode.org/download/72
• https://cldr.unicode.org/index/downloads/cldr-42
• https://github.com/unicode-org/icu/pull/2103