Migrate toolkit dependencies to ESM

[hidakatsuya]

Update actions/* packages.

[Copilot]

Pull request overview

Migrates this GitHub Action’s runtime code and @actions/* toolkit dependencies to ESM, aligning the source with modern Node execution and updated toolkit majors.

Changes:

• Bump @actions/core, @actions/exec, and @actions/tool-cache to newer major versions (and refresh lockfile transitive deps like undici/semver).
• Convert src/* files from CommonJS require to ESM import/named exports, including explicit .js extensions.
• Mark the package (and dist/) as ESM via "type": "module".

Reviewed changes

Copilot reviewed 4 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
yarn.lock	Updates lockfile entries for new @actions/* majors and related transitive dependencies.
package.json	Switches package to ESM (type: module) and bumps @actions/* dependency majors.
src/index.js	Uses ESM imports and refactors setup imports to named setup exports.
src/linux.js	Converts @actions/exec import to ESM.
src/windows.js	Converts imports to ESM and uses node:-prefixed built-ins.
dist/package.json	Ensures dist/ is treated as ESM by Node via local package scope.

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