t3033: avoid 'ambiguous refs' warning

t3033: avoid 'ambiguous refs' warning

Because "test_commit five" creates a commit and point it with a tag
'five', doing so on a branch whose name is 'five' will later result
in an 'ambiguous refs' warning.  Even though it is harmless because
all the later references are for the tag, there is no reason for the
branch to be called 'five'.  Give it a name that describes its
purpose more clearly, i.e. "newroot".

Signed-off-by: Junio C Hamano <redacted>