message: Prepare CHANGELOG for 1.0.4
diff: ## 1.0.4 - 28 Jun 2021
  -- Fix `RUNNER_TEMP environment variable must be set` when using runner.
  +- Fix `RUNNER_TEMP environment variable must be set` when using runner. [#594](https://github.com/github/codeql-action/pull/594)
  +- Fix couting of lines of code for C# projects. [#586](https://github.com/github/codeql-action/pull/586)
  +
  ## 1.0.3 - 23 Jun 2021
  No user facing changes.
  