git-blame-ignore-revs: Add previous commit

And enable use of the auto-rebase script: https://github.com/NixOS/nixpkgs/tree/master/maintainers/scripts/auto-rebase

Author: infinisil

.git-blame-ignore-revs

@@ -229,3 +229,6 @@ adb9714bd909df283c66bbd641bd631ff50a4260
 
 # tmuxPlugins sha-to-sri.py script
 516b1e74c358a9c4b06e5591f8c1a2897aad0c33
+
+# treewide format of all Nix files
+b4ae6694f7c65ed2fc9a8bad3855913354ee7a3f # !autorebase nix-shell --run treefmt