Build gix-diff with --no-default-features for WASM

But continue building default features of `gix-pack`.

Author: EliahKagan

.github/workflows/ci.yml

@@ -460,9 +460,8 @@ jobs:
       - name: crates with 'wasm' feature
         run: |
           set +x
-          for crate in gix-diff gix-pack; do
-            cargo build -p "$crate" --features wasm --target "$TARGET"
-          done
+          cargo build -p gix-diff --no-default-features --features wasm --target "$TARGET"
+          cargo build -p gix-pack --features wasm --target "$TARGET"
       - name: gix-pack with all features (including wasm)
         run: cargo build -p gix-pack --all-features --target "$TARGET"