Enable shorter block times rpc test

qa/pull-tester/rpc-tests.sh

@@ -77,8 +77,7 @@ testScripts=(
     'p2p_node_bloom.py'
     'regtest_signrawtransaction.py'
     'finalsaplingroot.py'
-    # TODO: enable the following test when updating PROTOCOL_VERSION in version.h for Blossom
-    # 'shorter_block_times.py'
+    'shorter_block_times.py'
     'sprout_sapling_migration.py'
     'turnstile.py'
 );