Merge bitcoin/bitcoin#22916: doc: add missing copyright header to getuniquepath.cpp

69a439b880 doc: add missing copyright header to getuniquepath.cpp (fanquake)

Pull request description:

  This was missed in #21052.

ACKs for top commit:
  hebasto:
    ACK 69a439b880, but a scripted-diff using `copyright_header.py insert` looks preferable.

Tree-SHA512: 1a75ffd93fa8e5e83821e1fe984353422740ebf9e203dc873debf4dffec0e23f55a1e31f806dd2d66087d3620f6dc447af69f9124f0bcc6676ef91ee35374832

src/util/getuniquepath.cpp

@@ -1,3 +1,7 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #include <random.h>
 #include <fs.h>
 #include <util/strencodings.h>