…/github dependency

Re: actions#1186

@dscho discovered that the checkout action could stall for a
considerable amount of time on Windows runners waiting for PowerShell
invocations made from 'windows-release' npm package to complete.

Then I studied the dependency chain to figure out where
'windows-release' was imported:

'@actions/checkout'@main
  <- '@actions/github'@2.2.0
    <- '@octokit/endpoint'@6.0.1
    <- '@octokit/graphql'@4.3.1
    <- '@octokit/request'@5.4.2
    <- '@octokit/rest'@16.43.1
      <- 'universal-user-agent'@4.0.1
        <- 'os-name'@3.1.0
          <- 'windows-release'@3.1.0

'universal-user-agent' package dropped its dependency on 'os-name' in
https://github.com/gr2m/universal-user-agent/releases/tag/v6.0.0 .

'@actions/github' v3 removed dependency on '@octokit/rest'@16.43.1 and
allows users to move away from the old 'universal-user-agent' v4.
(actions/toolkit#453)

This pull request attempts to update the version of '@actions/github'
used in the checkout action to avoid importing 'windows-release'.

Based on testing in my own repositories, I can see an improvement in
reduced wait time between entering the checkout action and git actually
starts to do useful work.