relnotes: add 6.7.1 stable 6.7.1

relnotes: add 6.7.1

--- a/relnotes/6.7	Sat Mar 16 21:02:19 2024 -0300
+++ b/relnotes/6.7	Thu Mar 21 12:23:25 2024 +0100
@@ -1,3 +1,12 @@
+= Mercurial 6.7.1 =
+
+Exceptional release following a crash found in delta code that can be triggered
+with complex repository shapes.
+
+ * delta-search: fix crash caused by unbound variable
+ * sshpeer: fix path when handling invalid url exception
+ * subrepo: fix normalizing paths with scheme
+
 = Mercurial 6.7 =
 
 As usual, a *lot* of patches don't make it to this list.