ci: add wasm32v1-none target and SKIP_WASM_BUILD to fix serde_core duplicate alloc error

The paritytech CI container lacks the wasm32v1-none target, causing
wasm-builder to fall back to wasm32-unknown-unknown with -Z build-std.
Combined with our serde_core fork, this creates a duplicate lang item
error for alloc crate.

Fix: Add rustup target add wasm32v1-none to all WASM-building jobs.
For check-only jobs (bench checks, docs, each-crate), add SKIP_WASM_BUILD=1.

Also fixes test-deterministic-wasm wasm blob path to work with either target.

.github/workflows/check-pezframe-omni-bencher.yml

@@ -34,6 +34,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
+      - name: Install wasm32v1-none target
+        run: rustup target add wasm32v1-none
+
       - name: Clean cargo cache to free disk space
         run: |
           cargo clean 2>/dev/null || true
@@ -86,6 +89,9 @@ jobs:
       - name: Checkout
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
 
+      - name: Install wasm32v1-none target
+        run: rustup target add wasm32v1-none
+
       - name: script (benchmark ${{ matrix.bench_cmd }})
         id: required
         shell: bash