`{format: false}` doesn't work with encoding conversion

[jameslan]

See:

libxml2-wasm/test/backend/encoding.spec.mts

Line 78 in d9f2119

it.skip('saves to specified encoding without format', () => {

The test case fails with the following message when enabled:

  1) encoding
       document save
         saves to specified encoding without format:

      AssertionError: expected '<?xml version="1.0" encoding="utf-8"?…' to equal '<?xml version="1.0" encoding="utf-8"?…'
      + expected - actual

       <?xml version="1.0" encoding="utf-8"?>
      -<levelone>
      -   <asdf RT="Müller"/>
      -</levelone>
      +<levelone><asdf RT="Müller"/></levelone>
      
      at Context.<anonymous> (file:///Users/james/sat/libxml2-wasm/test/backend/encoding.spec.mts:171:60)
      at process.processImmediate (node:internal/timers:505:21)