fix: relax Golang version requirement to run GitHub Action (#83)

* fix: relax Golang version requirement to run GitHub Action

Use a method to install the Golang conformance test client that doesn't
require Go 1.16+. This is important for Functions Framework Go, which
needs to test using multiple different versions of Go but currently
relies on the same version of Go to install the test client and run the
Framework itself.

* Don't use 'latest' string

Author: anniefu

action/README.md

@@ -3,13 +3,13 @@
 This action runs the Functions Framework conformance tests with the specified
 parameters.
 
-Requires Go 1.16+ to be installed prior to running (e.g. actions/setup-go).
+Requires Go to be installed prior to running (e.g. actions/setup-go).
 
 ## Inputs
 
 ### `version`
 
-The version of conformance tests to run. Default `latest`.
+The version of conformance tests to run. Default to latest release if unspecified.
 
 ### `cmd`
 

action/action.yml

@@ -2,8 +2,8 @@ name: 'Run conformance tests'
 description: 'Run the functions framework conformance tests with specified parameters.'
 inputs:
   version:
-    description: 'version of the conformance tests to run'
-    default: 'latest'
+    description: 'version of the conformance tests to run. Defaults to latest release if unspecified.'
+    default: ''
   outputFile:
     description: 'output file from function'
     default: 'function_output.json'