Fix undetected change bug in rename tests

tests/test-rename-merge2

@@ -5,7 +5,7 b' cd t'
 
 cat <<'EOF' > merge
 #!/bin/sh
-echo merge > $1
+echo merge $1 $2 $3 > $1
 EOF
 chmod +x merge
 

tests/test-rename-merge2.out

@@ -16,9 +16,9 b' my rev@e300d1c794ec other rev@735846fee2'
 0 files updated, 2 files merged, 0 files removed, 0 files unresolved
 (branch merge, don't forget to commit)
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+M a
 M b
   a
-C a
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