mail/exim*: update to 4.98.2 release (+)

This is a security release, addressing CVE-2025-30232

JH/01 Fix use-after-free notified by Trend Micro (ref: ZDI-CAN-26250).
Null out debug_pretrigger_buf pointer before freeing the buffer;
the use of this buffer by the storage management checks the pointer
for non-null before using it.

Security: CVE-2025-30232