design/24543: fix broken links

These two proposal docs link to a common background doc, but the link
URL was wrong.

Change-Id: Ib4a5d4cc2ffd42d9b7dd0098695c5db1ad55a263
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/219541
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: aclements

design/24543/conservative-inner-frame.md

@@ -13,7 +13,7 @@ safe-points only at function calls.
 We propose that the Go implementation switch to *non-cooperative*
 preemption.
 The background and rationale for this proposal are detailed in the
-[top-level proposal document](../20543-non-cooperative-preemption.md).
+[top-level proposal document](../24543-non-cooperative-preemption.md).
 
 This document details a specific approach to non-cooperative
 preemption that uses conservative GC techniques to find live pointers

design/24543/safe-points-everywhere.md

@@ -13,7 +13,7 @@ safe-points only at function calls.
 We propose that the Go implementation switch to *non-cooperative*
 preemption.
 The background and rationale for this proposal are detailed in the
-[top-level proposal document](../20543-non-cooperative-preemption.md).
+[top-level proposal document](../24543-non-cooperative-preemption.md).
 
 This document details a specific approach to non-cooperative
 preemption based on constructing stack and register maps at