_content/doc/go1.25: minor formatting fix

Change-Id: Id80e78f09a647c90f50808a43aea2aa8ac3025fd
Reviewed-on: https://go-review.googlesource.com/c/website/+/694137
Reviewed-by: Cherry Mui <[email protected]>
Auto-Submit: Austin Clements <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: aclements

_content/doc/go1.25.md

@@ -189,7 +189,7 @@ memory. This can be disabled with the [GODEBUG setting](/doc/godebug)
 
 ## Compiler {#compiler}
 
-### nil pointer bug
+### `nil` pointer bug
 
 <!-- https://go.dev/issue/72860, CL 657715 -->