fix(deps): Update core/actions to v3

[lourens-octopus]

[sc-138245]

@actions/core v3 is ESM-only. To support this, the project's toolchain was migrated to ESM:

tsconfig.json

• "module": "commonjs" → "module": "ESNext" so TypeScript emits ESM
• Added "moduleResolution": "bundler" (designed for webpack/ncc; no .js extensions needed on relative imports)
• "target": "es6" → "target": "ES2022" (appropriate for the Node.js 20 runtime)

package.json

• Bumped @actions/core to 3.0.0
• Jest: added extensionsToTreatAsEsm: [".ts"] and configured ts-jest with useESM: true
• Removed the transformIgnorePatterns override for msw — no longer needed as msw v2 is already ESM and loads natively in ESM mode
• Updated all test scripts to use node --experimental-vm-modules so Jest can load ESM modules at test time

No source code changes were required. The ncc bundler (webpack 5) continues to produce a standard CJS dist/index.js, so action.yml and the GitHub Actions
runtime are unaffected.

Successful run: https://github.com/OctopusDeployTesting/devex-action-tests/actions/runs/23269282819