blame: fix leaking data for blame scoreboards

There are some memory leaks when cleaning up blame scoreboards. Fix
those.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t8006-blame-textconv.sh

@@ -1,6 +1,8 @@
 #!/bin/sh
 
 test_description='git blame textconv support'
+
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 find_blame() {