Add Build tests workflow

[yegorich]

This workflow builds the package with both CMake and autoconf.

[yegorich]

@hyperrealm could you look at these warnings:

 YACC     grammar.c
/home/runner/work/libconfig/libconfig/lib/grammar.y:24.1-8: warning: POSIX Yacc does not support %defines [-Wyacc]
   24 | %defines
      | ^~~~~~~~
/home/runner/work/libconfig/libconfig/lib/grammar.y:25.1-7: warning: POSIX Yacc does not support %output [-Wyacc]
   25 | %output "y.tab.c"
      | ^~~~~~~
/home/runner/work/libconfig/libconfig/lib/grammar.y:25.9-17: warning: POSIX Yacc does not support string literals [-Wyacc]
   25 | %output "y.tab.c"
      |         ^~~~~~~~~
/home/runner/work/libconfig/libconfig/lib/grammar.y:26.1-12: warning: POSIX Yacc does not support %pure-parser [-Wyacc]
   26 | %pure-parser
      | ^~~~~~~~~~~~
/home/runner/work/libconfig/libconfig/lib/grammar.y:26.1-12: warning: deprecated directive: ‘%pure-parser’, use ‘%define api.pure’ [-Wdeprecated]
   26 | %pure-parser
      | ^~~~~~~~~~~~
      | %define api.pure
/home/runner/work/libconfig/libconfig/lib/grammar.y:95.1-11: warning: POSIX Yacc does not support %destructor [-Wyacc]
   95 | %destructor { free($$); } TOK_STRING
      | ^~~~~~~~~~~
/home/runner/work/libconfig/libconfig/lib/grammar.y: warning: fix-its can be applied.  Rerun with option '--update'. [-Wother]

[yegorich]

With this PR we can disable conan.yaml in GH menu untill someone has time and knowledge to fix it.

[hyperrealm]

Those warnings are not actionable as this package does not use POSIX yacc; it uses GNU bison.