switch to actions-toolkit implementation

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

src/state-helper.ts

@@ -1,12 +1,7 @@
 import * as core from '@actions/core';
 
-export const IsPost = !!process.env['STATE_isPost'];
 export const tmpDir = process.env['STATE_tmpDir'] || '';
 
 export function setTmpDir(tmpDir: string) {
   core.saveState('tmpDir', tmpDir);
 }
-
-if (!IsPost) {
-  core.saveState('isPost', 'true');
-}