tests: partially fix test-transaction-rollback-on-revlog-split.t on Windows

For whatever reason, the extra space causes different output on Windows:

    $ printf '% 20d' '1' | xxd -
    0000000: 2020 2020 2020 2020 2020 2020 2020 2020
    0000010: 2020 2020 31                                 1

vs WSL:

    /mnt/c/Users/Matt/hg/tests$ printf '% 20d' '1' | xxd -
    00000000: 2020 2020 2020 2020 2020 2020 2020 2020
    00000010: 2020 2031

Without the space, they both agree the last word is 2031.  There are other
failures on Windows that I don't understand that are introduced by 46b828b85eb7
and 18415fc918a1.

Differential Revision: https://phab.mercurial-scm.org/D10763

tests/test-transaction-rollback-on-revlog-split.t

@@ -28,9 +28,9 b' adding the big change.'
 
   $ hg init troffset-computation --config format.revlog-compression=none
   $ cd troffset-computation
-  $ printf '% 20d' '1' > file
+  $ printf '%20d' '1' > file
   $ hg commit -Aqm_
-  $ printf '% 1024d' '1' > file
+  $ printf '%1024d' '1' > file
   $ hg commit -Aqm_
   $ dd if=/dev/zero of=file bs=1k count=128 > /dev/null 2>&1
   $ hg commit -Aqm_