run_with_zodb3py2_compat was renamed to run_with_zodb4py2_compat in
nexedi/zodbtools@c59a54ca .

Without the fix go genrate was failing as

    (neo) (z-dev) (g.env) kirr@deca:~/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb/btree$ go generate
    Traceback (most recent call last):
      File "./testdata/gen-testdata", line 26, in <module>
        from zodbtools.test.gen_testdata import run_with_zodb3py2_compat
    ImportError: cannot import name run_with_zodb3py2_compat

and

    (neo) (z-dev) (g.env) kirr@deca:~/src/neo/src/lab.nexedi.com/kirr/neo/go/zodb$ go generate
    Traceback (most recent call last):
      File "./py/pydata-gen-testdata", line 24, in <module>
        from zodbtools.test.gen_testdata import run_with_zodb3py2_compat
    ImportError: cannot import name run_with_zodb3py2_compat

This amends commit fc69e00d (go/zodb/fs1: Fix Python database generator
to work with recent zodbtools).