Parser warnings with -Wyacc

[frozencemetery]

From CI logs:

/bin/bash ../ylwrap parser.y y.tab.c parser.c y.tab.h `echo parser.c | sed -e s/cc$/hh/ -e s/cpp$/hpp/ -e s/cxx$/hxx/ -e s/c++$/h++/ -e s/c$/h/` y.output parser.output -- bison -y -d 
/tmp/build/src/parser.y:46.14-19: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
   46 | %type <sval> STRING
      |              ^~~~~~
/tmp/build/src/parser.y:47.14-16: warning: POSIX yacc reserves %type to nonterminals [-Wyacc]
   47 | %type <ival> INT rule rule_start requiredkv
      |              ^~~
updating parser.h