community/*: add docbook-xsl-nons to makedepends, community/gxr: fix build with gcc 14 on 32-bit arches

• community/{gxr,telepathy-farstream,urfkill}: fix rebuild failure due to missing non-namepsaced version of docbook-xsl for xsl parsing by explicitly including the -nons subpackage. Errors found on the 3.21 builders. Ref: #16579 (closed) The error has been resolved with 50bfb70b, but it is still advisable to add a dependency on the variant.

• community/gxr: fix build with gcc 14 on 32-bit arches. Error found in CI.

../src/gxr-context.c: In function '_destroy_session':
../src/gxr-context.c:626:17: error: assignment to 'XrSession' {aka 'long long unsigned int'} from 'void *' makes integer from pointer without a cast [-Wint-conversion]
  626 |   self->session = NULL;
      |                 ^