test-profile: allow negative time in JSON output (issue5542)

I don't know why it can be a negative number, but that shouldn't be important
here.

tests/test-profile.t

@@ -90,7 +90,7 b' Various statprof formatters work'
 
   $ hg --profile --config profiling.statformat=json sleep 2>../out
   $ cat ../out
-  \[\[\d+.* (re)
+  \[\[-?\d+.* (re)
 
 statprof can be used as a standalone module