Use .zeek file suffix in unit tests

testing/btest/scripts/base/frameworks/control/configuration_update.zeek

@@ -7,7 +7,7 @@
 
 const test_var = "ORIGINAL VALUE (this should be printed out first)" &redef;
 
-@TEST-START-FILE test-redef.bro
+@TEST-START-FILE test-redef.zeek
 redef test_var = "NEW VALUE (this should be printed out second)";
 @TEST-END-FILE
 

testing/btest/scripts/base/frameworks/control/id_value.zeek

@@ -8,7 +8,7 @@
 # This value shouldn't ever be printed to the controllers stdout.
 const test_var = "Original value" &redef;
 
-@TEST-START-FILE only-for-controllee.bro
+@TEST-START-FILE only-for-controllee.zeek
 # This is only loaded on the controllee, but it's sent to the controller 
 # and should be printed there.
 redef test_var = "This is the value from the controllee";