update title to match Maria's comment/other templates

Author: eburdekin

.github/ISSUE_TEMPLATE/prework-pm.md

@@ -1,5 +1,5 @@
 ---
-title: "Self-Onboarding Product Manager:"
+title: "Pre-work: Product Manager"
 description: "An issue to help new developers get acquainted with our processes."
 name: "Pre-work: Product Manager"
 labels: feature: onboard / offboard, issue level I: request, priority: medium, role: product management, size: 1pt