tests: tweak chg test to make it fail less often

the test apparently sometimes prints the word "start" as a part of profile,
so let's no longer match "start":

   CHGHG=/*/install/bin/hg (glob)
+  \x1b[90m   | 50.0%  0.01s  profiling.py:   __enter__       line 196:  self.start()\x1b[0m (esc)
+  \x1b[90m   | 50.0%  0.01s  profiling.py:   start           line 261:  self._profiler.__enter__()\x1b[0m (esc)
+  \x1b[90m   | 50.0%  0.01s  profiling.py:   statprofile     line 125:  statprof.start(mechanism=b'...\x1b[0m (esc)
+  \x1b[90m   | 50.0%  0.01s  statprof.py:    start           line 356:  state.thread.start()\x1b[0m (esc)
+  \x1b[90m   | 50.0%  0.01s  threading.py:   start           line 852:  self._started.wait()\x1b[0m (esc)

tests/test-chg.t

@@ -561,12 +561,12 b' If CHGHG is not set, chg will set it bef'
   $ hg --kill-chg-daemon
   $ HG=$CHGHG CHGHG= CHGDEBUG= hg debugshell -c \
   >   'ui.write(b"CHGHG=%s\n" % ui.environ.get(b"CHGHG"))' 2>&1 \
-  >   | grep -E 'CHGHG|start'
+  >   | grep -E 'CHGHG|start cmdserver'
   chg: debug: * start cmdserver at * (glob)
   CHGHG=/*/install/bin/hg (glob)
 
 Running the same command a second time shouldn't spawn a new command server.
   $ HG=$CHGHG CHGHG= CHGDEBUG= hg debugshell -c \
   >   'ui.write(b"CHGHG=%s\n" % ui.environ.get(b"CHGHG"))' 2>&1 \
-  >   | grep -E 'CHGHG|start'
+  >   | grep -E 'CHGHG|start cmdserver'
   CHGHG=/*/install/bin/hg (glob)