Correct upload asset code (#1805)
Correct upload asset code (#1805)

1. Remove incorrect usage of await on synchronous method
2. Dispose of stream after use
shiftkey/octokit.net,alfhenrik/octokit.net,octokit/octokit.net,editor-tools/octokit.net,adamralph/octokit.net,editor-tools/octokit.net,alfhenrik/octokit.net,shiftkey/octokit.net,octokit/octokit.net