fix: rework setupShellCommand (#930)

* fix: rework `setupShellCommand`

* move all logic to separate function so we can test that later
* split `step.Shell` and `step.WorkingDirectory` setup into own funcs
* general cleanup of function
* use `ActPath` to not collide with checked out repository
* use `shellquote.Split()` instead of `strings.Fields()` for better command split
* replace single string concat with `fmt`

Signed-off-by: hackercat <me@hackerc.at>

* lint(editorconfig): ignore *_test.go due to mixed style

Signed-off-by: hackercat <me@hackerc.at>

act/model/workflow_test.go

@@ -266,6 +266,7 @@ func TestStep_ShellCommand(t *testing.T) {
 		shell string
 		want  string
 	}{
+		{"pwsh -v '. {0}'", "pwsh -v '. {0}'"},
 		{"pwsh", "pwsh -command . '{0}'"},
 		{"powershell", "powershell -command . '{0}'"},
 	}