encode_keep_buffer test fails with Lua 5.5

[mcepl]

While enabling Lua 5.5 builds for all our packages in openSUSE, I was hit by this failed test when running the test suite:

[    5s] Executing(%check): /usr/bin/bash -e /var/tmp/rpm-tmp.o7eCaZ
[    5s] + umask 022
[    5s] + cd /home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build
[    5s] + cd lua-cjson-2.1.0.16
[    5s] + rm -rf build
[    5s] + export 'LUA_CPATH=/home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build/BUILDROOT/usr/lib64/lua/5.5/?.so;;'
[    5s] + LUA_CPATH='/home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build/BUILDROOT/usr/lib64/lua/5.5/?.so;;'
[    5s] + export 'LUA_PATH=/home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build/BUILDROOT/usr/share/lua/5.5/?.lua;/home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build/BUILDROOT/usr/share/lua/5.5/?/init.lua;;'
[    5s] + LUA_PATH='/home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build/BUILDROOT/usr/share/lua/5.5/?.lua;/home/abuild/rpmbuild/BUILD/lua55-cjson-2.1.0.16-build/BUILDROOT/usr/share/lua/5.5/?/init.lua;;'
[    5s] + cd tests
[    5s] + set -o pipefail
[    5s] + perl ./genutf8.pl
[    5s] + lua -e 'print("Testing Lua CJSON version " .. require("cjson")._VERSION)'
[    5s] Testing Lua CJSON version 2.1.0.11
[    5s] + ./test.lua
[    5s] + grep -E -A 3 'FAIL|Summary'
[    5s] + cut -c -150
[    5s] ==> Test [95] Set encode_keep_buffer(nil, true) [throw error]: FAIL
[    5s] [Input] { nil, true }
[    5s] [Expected:error] { ONE_OF{ "bad argument #2 to '?' (found too many arguments)", "bad argument #2 to 'cjson.encode_keep_buffer' (found too many argumen
[    5s] [Received:success] { true }
[    5s] --
[    5s] ==> Summary: 1/105 tests failed

(I cannot use ./runtests.sh, because I need to test on library already build and installed to temporary location; also, it seems that the version number has not been updated, but that is not important).

Tests pass on Lua 5.3, Lua 5.4, and with OpenResty/LuaJIT

Complete build log with all details of packages used and steps for reproduction.