fix multiline outputs

[alexrashed]

This PR reverts a small change introduced with 84f77c4 where setting the action's output has been changed from using @actions/core's setOutput function to writing the output to process.env.GITHUB_OUTPUT:

actions-find-and-replace-string/index.js

Line 11 in 84f77c4

fs.writeFileSync(process.env.GITHUB_OUTPUT, `value=${resultValue}\n`)

This is exactly how it's described in GitHub's blog announcing the deprecation: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

However, this does not work for multiline outputs, as they now fail with an error similar to this:

...
Run mad9000/actions-find-and-replace-string@3
##[debug]Node Action run completed with exit code 0
##[debug]Set output value = <first-output-line>
Error: Unable to process file command 'output' successfully.
Error: Invalid format '<second-output-line>'
##[debug]System.Exception: Invalid format '<second-output-line>'
##[debug]   at GitHub.Runner.Worker.EnvFileKeyValuePairs.GetEnumerator()+MoveNext()
##[debug]   at GitHub.Runner.Worker.SetOutputFileCommand.ProcessCommand(IExecutionContext context, String filePath, ContainerInfo container)
##[debug]   at GitHub.Runner.Worker.FileCommandManager.ProcessFiles(IExecutionContext context, ContainerInfo container)
##[debug]Finishing: <workflow-step-name>
...

In fact, the @action/core library provided by GitHub has been updated a few days before the deprecation was announced such that setOutput uses the new file-based mechanism (and correctly handles multi-line outputs by using an EOF-delimiter based approach): actions/toolkit#1178
This change is contained in @action/core==1.10.0, which is already being used by this action.

Long story short: This PR reverts this change to use setOutput provided by @actions/core again, which should fix issues with multi-line outputs.