Is it possible to skip a file rename when it's not there in Automator?
I wrote a small JavaScript for Automation program that may be able to accomplish what you want to do. It checks for and deletes the existing file, then proceeds to download the desired file from the GIT repository:

// Get Finder application
finder = Application('Finder')
finder.includeStandardAdditions = true

// Create path to the location of the existing file
path = Path("path/to/destination")

// Check to see if the old file exists
if (finder.files.length &gt; 0) {
    oldFile = finder.files[0]
    oldFile.delete()
}

// Use curl to download the new file
current = Application.currentApplication()
current.includeStandardAdditions = true
theURL = "http://url/to/git/plugin"
current.doShellScript("curl -L " + theURL + " -o " + path.toString())


Alternatively, you could take some portion of this code (such as the conditional that determines whether there is an existing file) and put it into an Automator "Run JavaScript" action in your existing script.