test: enable sparse-revlog for test-lfconvert.t

We are about to enable sparse-revlog globally. To help with reviewing the
tests change, we isolate them in individual changesets.

Differential Revision: https://phab.mercurial-scm.org/D5322

tests/test-lfconvert.t

@@ -1,3 +1,9 b''
+TRANSITIONAL CONFIG
+  $ cat << EOF >> $HGRCPATH
+  > [format]
+  > sparse-revlog = yes
+  > EOF
+
   $ USERCACHE="$TESTTMP/cache"; export USERCACHE
   $ mkdir "${USERCACHE}"
   $ cat >> $HGRCPATH <<EOF
@@ -100,6 +106,7 b' Test link+rename largefile codepath'
   generaldelta
   largefiles
   revlogv1
+  sparserevlog
   store
   testonly-simplestore (reposimplestore !)