chore: resolve incomplete/missing copyright headers in unit tests

Author: kwvg

src/test/cachemap_tests.cpp

@@ -1,4 +1,6 @@
 // Copyright (c) 2014-2023 The Dash Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <cachemap.h>
 #include <streams.h>

src/test/cachemultimap_tests.cpp

@@ -1,4 +1,6 @@
 // Copyright (c) 2014-2023 The Dash Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <cachemultimap.h>
 #include <streams.h>

src/test/evo_islock_tests.cpp

@@ -1,3 +1,7 @@
+// Copyright (c) 2025 The Dash Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
 #include <consensus/consensus.h>
 #include <hash.h>
 #include <instantsend/lock.h>

src/test/governance_validators_tests.cpp

@@ -1,4 +1,6 @@
 // Copyright (c) 2014-2023 The Dash Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <governance/validators.h>
 #include <util/strencodings.h>

src/test/ratecheck_tests.cpp

@@ -1,4 +1,6 @@
 // Copyright (c) 2014-2022 The Dash Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <governance/governance.h>