Update to wit-bindgen 0.12.0.

In particular, this has bytecodealliance/wit-bindgen#670, which fixes a
bug hit by `poll-list`.

Author: sunfishcode

README.md

@@ -23,6 +23,6 @@ jobs:
     - uses: actions/checkout@v3
     - uses: WebAssembly/wit-abi-up-to-date@v14
       with:
-        wit-bindgen: '0.11.0'
+        wit-bindgen: '0.12.0'
         worlds: 'command reactor'
 ```

action.yml

@@ -5,7 +5,7 @@ inputs:
   wit-bindgen:
     description: 'version of the `wit-bindgen` tool to use'
     required: false
-    default: '0.11.0'
+    default: '0.12.0'
   worlds:
     description: 'worlds to generate documentation for'
     required: false