backport of commit ed204e0fd985bbb43da7e19e07cf541ad74284a8 (#18670)

Co-authored-by: Luiz Aoqui <luiz@hashicorp.com>

.changelog/18662.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+client: prevent tasks from starting without the prestart hooks running
+```

client/allocrunner/taskrunner/task_runner.go

@@ -591,6 +591,12 @@ MAIN:
 			goto RESTART
 		}
 
+		// Check for a terminal allocation once more before proceeding as the
+		// prestart hooks may have been skipped.
+		if tr.shouldShutdown() {
+			break MAIN
+		}
+
 		select {
 		case <-tr.killCtx.Done():
 			break MAIN