docs: add CHANGES entries for #408, #409, #410, #412, #416

[thegushi]

Summary

Catches up CHANGES-202605.md with five recently merged PRs:

• fix: heap-allocate large mlfi_eom() locals to prevent SIGBUS on macOS #410 — SIGBUS crash in mlfi_eom on macOS ARM64 (Security/correctness)
• fix: declare opendmarc_policy_fetch_fo() in dmarc.h.in (#407) #408 — opendmarc_policy_fetch_fo() missing from public header (Build system)
• ci: add macOS build and test job (#407) #409 — macOS CI job added (Build system)
• tests: gate t-verify-self-spf on TEST_SPF conditional (#411) #412 — t-verify-self-spf gated on TEST_SPF (Build system)
• warn when PublicSuffixList is more than 6 months old #416 — Stale PublicSuffixList warning (Utilities and minor fixes)

The #408/#409/#410/#412 entries were drafted on the chore/changes-sigbus-spf-gate branch; #416 is new.