lang/ruby33: Fix build with latest -CURRENT

post-install-DOCS-on copies all files/directories under ${WRKSRC}/doc/
into ${STAGEDIR}${RUBY_DOCDIR}/, then installs ${WRKSRC}/ChangeLog to
same directory. But there is ChangeLog directory under ${WRKSRC}/doc/.
As a result there is already ${STAGEDIR}${RUBY_DOCDIR}/ChangeLog
directory when ${WRKSRC}/ChangeLog is tried to be installed as
${WRKSRC}/doc/ChangeLog. Previously install(1) regards it as non-fatal
and build continues. But on latest -CURRENT the command regards it as
fatal and results in build error. So fix it by moving
${WRKSRC}/ChangeLog to ${WRKSRC}/doc/ChangeLog/ChangeLog at extract
phase.

Bump PORTREVISION as plist is changed.

PR: 278554
Reported by: Siva Mahadevan
MFH: 2024Q2