HTTP: fixed GCC 15 build with -Wunterminated-string-initialization.

HTTP: fixed GCC 15 build with -Wunterminated-string-initialization.

ngx_http_js_module.c:936:22: error: initializer-string for array of ‘char’ truncates NUL terminator
 but destination lacks ‘nonstring’ attribute (16 chars into 15 available) [-Werror=unterminated-string-initialization]
  936 |             .value = "PeriodicSession",
      |                      ^~~~~~~~~~~~~~~~~