Drop Node.js v20 from CI matrix

Context

Node.js v20 reaches EOL on April 30, 2026. Additionally, Node-API version 10 is not fully supported on v20 — the NAPI_PREAMBLE macro only returns napi_cannot_run_js for NAPI_VERSION_EXPERIMENTAL, not for version 10+. This was fixed in nodejs/node#55676 ("node-api: define version 10"), which landed in v22.14.0+ but was never backported to v20.

This causes test_cannot_run_js (and potentially other tests targeting Node-API v10) to crash with SIGSEGV on v20, as seen in #28.

Proposal

Remove 20.x from the CI test matrix in .github/workflows/test.yml, along with the Node 20-specific amaro/TypeScript stripping workaround.

.github/workflows/test.yml を確認し、まず CI テストマトリクスと、Node 20 固有の amaro/TypeScript stripping workaround を調べます。20.x のエントリとその workaround を削除します。workflow が v20 固有の処理なしで残りの Node.js バージョンを対象にすれば完了です。