test-convert-git: be tolerant to git output variants

tests/test-convert-git

@@ -181,6 +181,6 b" for root, dirs, files in os.walk('git-re"
 EOF
 python damage.py
 hg convert git-repo4 git-repo4-broken-hg 2>&1 | \
-    sed 's/fatal:.*/fatal: git error/g'
+    grep 'abort:' | sed 's/abort:.*/abort:/g'
 
 true

tests/test-convert-git.out

@@ -128,10 +128,4 b' addfoo'
 initializing destination git-repo4-sourcesort-hg repository
 abort: --sourcesort is not supported by this data source
 % damage git repository and convert again
-fatal: git error
-initializing destination git-repo4-broken-hg repository
-scanning source...
-sorting...
-converting...
-1 addfoo
-abort: cannot read changes in 6a101ac3f6d8b2524a64295ffd9be87ed927bfeb
+abort: