devel/doxygen: Fix TinyDeflate's clang-19 compatibility

Clang >= 19.0 requires a template argument list after the template
keyword for CWG96 compliance, see
https://github.com/llvm/llvm-project/pull/80801

Obtained from: Bernhard Rosenkränzer, via
https://github.com/bisqwit/TinyDeflate/commit/68ced8bd5c819264e628d4f063500753b77f613d

PR: 259331 (comment #6)
Reported by: Tamaoki Aoki
Approved by: portmgr@ (blanket approval for fixing broken builds)

(cherry picked from commit 4bd9003d8ca98b85964a07b23454f3c2607e191b)