chore(osv): keep the ledger header's self-description true while an entry stands

The header said the ledger "currently holds ZERO exemptions", which
stops being true the moment the sprintf-js entry lands. It now states
zero as the intended steady state and says every entry is a dated
exception with its own renewal date. The rest of the header is
byte-identical.

Claude-Session: https://claude.ai/code/session_01VF48aw8RPG6wzDnMgp6rtw
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

osv-scanner.toml

@@ -8,8 +8,9 @@
 # yet, where the alternative is pinning a required check red indefinitely, and
 # a permanently red required check is worth exactly as much as no scan at all.
 #
-# This ledger currently holds ZERO exemptions. That is the intended steady
-# state, not a coincidence — read the whole header before you change it.
+# This ledger's intended steady state is ZERO exemptions, not a coincidence:
+# every entry below is a dated exception with its own renewal date. Read the
+# whole header before you change it.
 #
 # ---------------------------------------------------------------------------
 # Three conventions govern every entry (decided on #4965)