Fix test_libhttp2 build issue of 8.1.x on Debian/Ubuntu

We don't see this issue on master, because we got rid of TCL.

Author: masaori335

proxy/http2/Makefile.am

@@ -76,6 +76,7 @@ test_libhttp2_LDADD = \
 	$(top_builddir)/lib/records/librecords_p.a \
 	$(top_builddir)/mgmt/libmgmt_p.la \
 	$(top_builddir)/proxy/shared/libUglyLogStubs.a \
+	@LIBTCL@ \
 	@HWLOC_LIBS@
 
 test_libhttp2_CPPFLAGS = $(AM_CPPFLAGS)\