WASM Build Test Fails with TypeError: Cannot read properties of undefined (reading 'set')

**Describe the bug**
When trying to build the wasm (WebAssembly) module, an error in a single test occurs:
```
4808/4818 Test #4818: test_wasm_jxl_decoder ............................................................................................................................................................................................................***Failed    0.15 sec
Running testSdr
/---/libjxl/tools/wasm_demo/jxl_decoder_test.js:47
  jxlModule.HEAP8.set(encoded, buffer);
                  ^

TypeError: Cannot read properties of undefined (reading 'set')
    at testSdr (/---/libjxl/tools/wasm_demo/jxl_decoder_test.js:47:19)
    at runTest (/---/libjxl/tools/wasm_demo/jxl_decoder_test.js:15:3)
    at Array.forEach (<anonymous>)
    at /---/libjxl/tools/wasm_demo/jxl_decoder_test.js:138:9

Node.js v22.15.1
```

**To Reproduce**
Run WASM build (with or without SIMD):
`BUILD_TARGET=wasm32 ENABLE_WASM_SIMD=1 emconfigure ./ci.sh release`

**Expected behavior**
The test should pass.

**Environment**
 - OS: OpenSUSE Tumbleweed
 - Compiler version: Clang 22.0.0, Emscripten/EMSDK 4.0.20
 - CPU type: x86-64
 - cjxl/djxl version string: cjxl 0.11.1 | SIMD supported: SSE, SSE2, SSE3, SSE4.1, SSE4.2, AVX, AVX2, Scalar

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