Pam Grier doesn’t look back that often. If she did, she said this week from New Mexico, “I’d be drinking.”But when Turner Classic Movies host Ben Mankiewicz called to ask if she’d consider being the focus of the new season of his podcast “The Plot Thickens,” she knew she had to do it. She’d listened to and loved the previous season that explored the career of Peter Bogdanovich and had an idea of what it would entail.