Fix test that fails 1 in 60 times

This test looks for how many times the string `50` appears in the text
of the `<main>` element of the page. The `<main>` element also contains
some times, for example 1:23pm.

This means that when the time reaches 1:50pm, 2:50pm, etc the number of
times the string `50` appears in the page changes. Which causes the test
assertions to fail.

tests/app/main/views/test_dashboard.py

@@ -552,8 +552,11 @@ def test_should_not_show_recent_templates_on_dashboard_if_only_one_template_used
     # count appears as total, but not per template
     expected_count = stats[0]['count']
     assert expected_count == 50
-    assert main.count(str(expected_count)) == 1
-    assert '50 text messages sent' in normalize_spaces(main)
+    assert normalize_spaces(
+        page.select_one('#total-sms .big-number').text
+    ) == (
+        '{} text messages sent'.format(expected_count)
+    )
 
 
 @freeze_time("2016-07-01 12:00")  # 4 months into 2016 financial year