fix: restore accidentally removed bool TMPL_INST in rpc/util.cpp

Commit a3e6fdd ('test: fix test assertions after backport')
accidentally removed the TMPL_INST(CheckRequiredOrDefault, bool, ...)
line that was added in 1e7166e. This caused linker errors across
multiple CI build configurations (nowallet, ubsan, fuzz, tsan,
multiprocess) due to the missing ArgValue<bool> template instantiation.

Restore the line in its correct position.

Author: thepastaclaw

src/rpc/util.cpp

@@ -579,6 +579,7 @@ TMPL_INST(nullptr, std::optional<bool>, maybe_arg ? std::optional{maybe_arg->get
 TMPL_INST(nullptr, const std::string*, maybe_arg ? &maybe_arg->get_str() : nullptr;);
 
 // Required arg or optional arg with default value.
+TMPL_INST(CheckRequiredOrDefault, bool, CHECK_NONFATAL(maybe_arg)->get_bool(););
 TMPL_INST(CheckRequiredOrDefault, int, CHECK_NONFATAL(maybe_arg)->getInt<int>(););
 TMPL_INST(CheckRequiredOrDefault, uint64_t, CHECK_NONFATAL(maybe_arg)->getInt<uint64_t>(););
 TMPL_INST(CheckRequiredOrDefault, const std::string&, CHECK_NONFATAL(maybe_arg)->get_str(););