Add a .git-blame-ingore-revs entry for edition 2021 changes

Ignore 643182f ("Automatic migration to Rust edition 2021") since this
performed a lot of trivial changes to a large percent of the repository.

(backport <#4154>)
(cherry picked from commit d694a4d)

[ adjusted the commit hash to be relevant to this branch - Trevor ]

Author: tgross35

.git-blame-ignore-revs

@@ -1,2 +1,5 @@
 # Format macro bodies
 50f26e08e146b7e9c7d1af9614486eba327d1e31
+
+# Automated changes to upgrade to the 2021 edition
+643182f7da26cedb09349b8bb3735c2e58ba24e6