chore: omit test files from published package

[legobeat]

From this:

npm notice package: @metamask/safe-event-emitter@3.1.1
npm notice === Tarball Contents ===
npm notice 739B  LICENSE
npm notice 2.1kB dist/cjs/index.js
npm notice 2.5kB dist/cjs/index.test.js
npm notice 1.7kB package.json
npm notice 1.9kB dist/cjs/index.js.map
npm notice 1.9kB dist/esm/index.mjs.map
npm notice 3.0kB dist/cjs/index.test.js.map
npm notice 3.0kB dist/esm/index.test.mjs.map
npm notice 1.1kB CHANGELOG.md
npm notice 1.3kB README.md
npm notice 2.0kB dist/esm/index.mjs
npm notice 2.5kB dist/esm/index.test.mjs
npm notice 182B  dist/cjs/index.d.ts
npm notice 182B  dist/esm/index.d.ts
npm notice 11B   dist/cjs/index.test.d.ts
npm notice 11B   dist/esm/index.test.d.ts
npm notice === Tarball Details ===
npm notice name:          @metamask/safe-event-emitter
npm notice version:       3.1.1
npm notice package size:  5.1 kB
npm notice unpacked size: 24.1 kB
npm notice shasum:        e89b840a7af8097a8ed4953d8dc8470d1302d3ef
npm notice integrity:     sha512-ihb3B0T/wJm1e[...]PqygCpgeniKMw==
npm notice total files:   16

to this:

npm notice package: @metamask/safe-event-emitter@3.1.1
npm notice === Tarball Contents ===
npm notice 739B  LICENSE
npm notice 2.1kB dist/cjs/index.js
npm notice 1.7kB package.json
npm notice 1.9kB dist/cjs/index.js.map
npm notice 1.9kB dist/esm/index.mjs.map
npm notice 1.1kB CHANGELOG.md
npm notice 1.3kB README.md
npm notice 2.0kB dist/esm/index.mjs
npm notice 182B  dist/cjs/index.d.ts
npm notice 182B  dist/esm/index.d.ts
npm notice === Tarball Details ===
npm notice name:          @metamask/safe-event-emitter
npm notice version:       3.1.1
npm notice package size:  4.0 kB
npm notice unpacked size: 13.1 kB
npm notice shasum:        11dcb6bd7e68f19c86b2d6984f90af413a8b0cb5
npm notice integrity:     sha512-onQvYMdzbPf9z[...]Fl0OQGjQ7jfTw==
npm notice total files:   10

[Mrtenz]

Cool. I didn't know you could exclude files like this.