CI: Fix failure on macos 26

Updated clang gives warnings:

/Users/runner/work/AtomVM/AtomVM/src/platforms/generic_unix/lib/sys.c:484:40: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
  484 |             char port_driver_name[64 + strlen("avm_"
      |                                   ~~~~~^~~~~~~~~~~~~
  485 |                                               "_port_driver.so")
      |                                               ~~~~~~~~~~~~~~~~~~
  486 |                 + 1];
      |                 ~~~
/Users/runner/work/AtomVM/AtomVM/src/platforms/generic_unix/lib/sys.c:493:41: error: variable length array folded to constant array as an extension [-Werror,-Wgnu-folding-constant]
  493 |         char port_driver_func_name[64 + strlen("_create_port") + 1];
      |                                    ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
2 errors generated.

Signed-off-by: Peter M <petermm@gmail.com>

Author: petermm

src/platforms/generic_unix/lib/sys.c

@@ -525,16 +525,14 @@ Context *sys_create_port(GlobalContext *glb, const char *driver_name, term opts)
 #ifdef DYNLOAD_PORT_DRIVERS
         void *handle;
         {
-            char port_driver_name[64 + strlen("avm_"
-                                              "_port_driver.so")
-                + 1];
+            char port_driver_name[64 + sizeof("avm_") - 1 + sizeof("_port_driver.so") - 1 + 1];
             snprintf(port_driver_name, sizeof(port_driver_name), "./avm_%s_port_driver.so", driver_name);
             handle = dlopen(port_driver_name, RTLD_NOW);
             if (!handle) {
                 return NULL;
             }
         }
-        char port_driver_func_name[64 + strlen("_create_port") + 1];
+        char port_driver_func_name[64 + sizeof("_create_port") - 1 + 1];
         snprintf(port_driver_func_name, sizeof(port_driver_func_name), "%s_create_port", driver_name);
         create_port_t create_port
             = (create_port_t) CAST_VOID_TO_FUNC_PTR(dlsym(handle, port_driver_func_name));