build(clang-analyzer): suppress clang-analyzer-security.ArrayBound

Problem:
clang 21 promoted alpha.security.ArrayBoundV2 to security.ArrayBound
(stable). This new check reports false-positive "out of bound access"
errors in drawline.c and vimscript.c, where the analyzer constructs
impossible paths (e.g. concealed line with draw_text=false yet ptr
advanced past the NUL terminator, or root AST node with a "next"
sibling).

Per-line NOLINT suppression doesn't work because the analyzer finds
multiple paths to the same false positive.

Solution:
Disable clang-analyzer-security.ArrayBound globally in the
clang-analyzer cmake target until the check matures.

Co-Authored-By: Claude

src/nvim/api/vimscript.c

@@ -545,6 +545,9 @@ Dict nvim_parse_expression(String expr, String flags, Boolean highlight, Arena *
           .ret_node_p = &children_array.items[0],
         }));
       } else if (node->next != NULL) {
+        // ret_node_p + 1 is valid: we're in a children_array (root node never
+        // has "next"). kv_size > 1 confirms we're not at root.
+        assert(kv_size(ast_conv_stack) > 1);
         kvi_push(ast_conv_stack, ((ExprASTConvStackItem) {
           .node_p = &node->next,
           .ret_node_p = cur_item.ret_node_p + 1,