Unshallow on fetch

src/git-command-manager.ts

@@ -1,5 +1,7 @@
 import * as exec from '@actions/exec'
 import * as io from '@actions/io'
+import * as fshelper from './fs-helper'
+import * as path from 'path'
 
 const tagsRefSpec = '+refs/tags/*:refs/tags/*'
 
@@ -114,6 +116,13 @@ export class GitCommandManager {
     }
 
     args.push('--progress', '--no-recurse-submodules')
+    if (
+      fshelper.fileExistsSync(
+        path.join(this.workingDirectory, '.git', 'shallow')
+      )
+    ) {
+      args.push('--unshallow')
+    }
 
     if (options) {
       args.push(...options)