NFC: Fix doc comment link in UndirectedGraph.swift (#7832)

`UndirectedGraph` uses an adjacency matrix not adjacency list for edges representation. The link in its doc comment should be corrected.

Author: MaxDesiatov

Sources/Basics/Graph/UndirectedGraph.swift

@@ -12,7 +12,7 @@
 
 import struct DequeModule.Deque
 
-/// Undirected graph that stores edges in an [adjacency matrix](https://en.wikipedia.org/wiki/Adjacency_list).
+/// Undirected graph that stores edges in an [adjacency matrix](https://en.wikipedia.org/wiki/Adjacency_matrix).
 @_spi(DontAdoptOutsideOfSwiftPMExposedForBenchmarksAndTestsOnly)
 public struct UndirectedGraph<Node> {
     public init(nodes: [Node]) {