Set $wgUseTidy = false on TextContentTest

If $wgUseTidy = true on LocalSettings, although this test
runs fine standalone, when batched with other database tests
it can fail with:
 --- Expected
 +++ Actual
 @@ @@
 -'<p>hello <i>world</i>
 -</p>'
 +'<p>hello <i>world</i></p>'

Change-Id: Id143abf45def7bb686f00584d3f7838dc7396ad7
Merge "Set $wgUseTidy = false on TextContentTest"