--function-context shows wrong function in chunk

When using --function-context, the function that is claimed at the top
of the diff does not match the actual function.

Note that the change exists in main, but the hunk header
(terminology?) shows other_routine.

$ git --version
git version 2.27.0

$ git diff -b --function-context

diff --git i/example.c w/example.c
index d87b59b..346e2a7 100644
--- i/example.c
+++ w/example.c

@@ -4,5 +4,5 @@ int other_routine() {
 }

 int main() {
-
+    puts("Hello, world!");
 }

Zach Riggle