Relative path does not work, also error throws exception

Describe the bug

Context: @actions/artifact

According to README.md, relative paths for files are supported as well as absolute path. However, when trying to use relative path I kept running into fatal error:

Error: File <file> does not exist

Also, if file is not found, the error is thrown even if I use continueOnError: true which is contrary to the docs:

If set to true and an error is encountered, the failed file will be skipped and ignored and all other queued files will be attempted to be uploaded.

I've tried try...catch but that did not work either.

I believe the error is due to how path is being checked:

https://github.com/actions/toolkit/blob/c9dab8c79daa06e0897ededaf7de9c351d22fec3/packages/artifact/src/internal/upload/upload-zip-specification.ts#L41-L44

https://github.com/actions/toolkit/blob/c9dab8c79daa06e0897ededaf7de9c351d22fec3/packages/artifact/src/internal/upload/upload-zip-specification.ts#L77-L80

As you can see, rootDirectory is not concatenated with filesToZip.

To Reproduce

const client = artifact.create();
const filePath = path.resolve(__dirname, 'file');
this.spawnSync.call('touch', [filePath]);
fs.openSync(filePath, 'a');
this.spawnSync.call('ls', ['-l', __dirname]);
console.log(fs.existsSync(filePath));
client.uploadArtifact('file-abs-path', [filePath], __dirname, { 
continueOnError: true }); // works
client.uploadArtifact('file-rel-path', ['file'], __dirname, { 
continueOnError: true }); // does not work, throws error

Expected behavior

• relative path to be functional
• continueOnError: true to not throw error

Start in packages/artifact/src/internal/upload/upload-zip-specification.ts at the referenced path checks, then reproduce the behavior with client.uploadArtifact using a relative file and continueOnError: true. Done means relative paths upload successfully and missing files are skipped without throwing when continueOnError is enabled.