Fix alloyio workflow build step

[carterworks]

The alloyio workflow currently invokes Rollup with --environment SANDBOX, but the browser package only exports configs when its expected build flags are set. That leaves CI with an empty Rollup config and the deploy job stops before the sandbox build.

Switch this step to pnpm --filter @adobe/alloy run build so the workflow uses the package's supported build entrypoint and produces the artifacts the sandbox build expects.

Validated locally with pnpm --filter @adobe/alloy run build && pnpm --filter @adobe/alloy-sandbox-browser run build.

[changeset-bot]

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Latest commit: 75442ce

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