tests: de-flake test-run-tests.t's "--jobs=2 --first" test

Once in a while, test-nothing.t finished before test-failure.t or
test-failure-copy.t (I haven't checked which one actually gets run
first). Since there already are two tests that will fail in the same
way, just run those two instead so the diff will be reproducible and
not timing-dependent.

The test case was added in 9a20f53e436f (run-tests: handle --jobs and
--first gracefully, 2014-10-09), and I have checked that backing that
out results in two failures being printed. Note that the summary may
still include multiple tests even if --first is given, it's just that
the diff is only printed for the first failure.

Differential Revision: https://phab.mercurial-scm.org/D1186

tests/test-run-tests.t

@@ -609,10 +609,7 b' Parallel runs'
   [1]
 
 failures in parallel with --first should only print one failure
-  >>> f = open('test-nothing.t', 'w')
-  >>> f.write('foo\n' * 1024) and None
-  >>> f.write('  $ sleep 1') and None
-  $ rt --jobs 2 --first
+  $ rt --jobs 2 --first test-failure*.t
   
   --- $TESTTMP/test-failure*.t (glob)
   +++ $TESTTMP/test-failure*.t.err (glob)
@@ -625,14 +622,14 b' failures in parallel with --first should'
    pad pad pad pad............................................................
   
   Failed test-failure*.t: output changed (glob)
-  Failed test-nothing.t: output changed
+  Failed test-failure*.t: output changed (glob)
   # Ran 2 tests, 0 skipped, 2 failed.
   python hash seed: * (glob)
   [1]
 
 
 (delete the duplicated test file)
-  $ rm test-failure-copy.t test-nothing.t
+  $ rm test-failure-copy.t
 
 
 Interactive run