Fix and cleanup of v2 setup actions

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

setup-buildx/src/state-helper.ts

@@ -1,7 +1,7 @@
 import * as core from '@actions/core';
 
 export const IsPost = !!process.env['STATE_isPost'];
-export const builderName = !!process.env['STATE_builderName'];
+export const builderName = process.env['STATE_builderName'] || '';
 
 export function setBuilderName(builderName: string) {
   core.saveState('builderName', builderName);