Update ci.yaml (#888)

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## Motivation and Context
<!-- Why is this change required? What problem does it solve? -->
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This PR removes CI from pull requests and runs it exclusively on main.

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.

.github/workflows/ci.yaml

@@ -1,7 +1,5 @@
 on:
-  pull_request:
-    paths-ignore:
-      - 'aws-models/**'
+  push:
     branches:
       - main
 
@@ -94,6 +92,7 @@ jobs:
       - uses: dtolnay/rust-toolchain@master
         with:
           toolchain: ${{ matrix.rust_version }}
+          targets: wasm32-unknown-unknown
       # Pinned to the commit hash of v2.1.0
       - uses: Swatinem/rust-cache@b894d59a8d236e2979b247b80dac8d053ab340dd
         with: