Don't run all tests when files end in a colon.

If running `bin/rails t test/models/bunny_test.rb:` we'd implicitly run all the
tests in the bunny test. I now highly doubt that people would ever put in a line
filter without a line *and* want that to mean run all tests in that file.

Instead, change regex to require a line digit after the colon, so runs without a
line at the end would fail to require the test file.

This also has the side benefit of breaking requiring a file with many colons:
`bin/rails t test/models/bunny_test.rb:::::::::::::4`

Think this means I've had enough colonoscopy to last me through the year :)

railties/lib/rails/test_unit/test_requirer.rb

@@ -15,7 +15,7 @@ def require_files(patterns)
       private
         def expand_patterns(patterns)
           patterns.map do |arg|
-            arg = arg.gsub(/(:\d*)+?$/, '')
+            arg = arg.gsub(/(:\d+)+?$/, '')
             if Dir.exist?(arg)
               "#{arg}/**/*_test.rb"
             else

railties/test/application/test_runner_test.rb

@@ -382,14 +382,6 @@ def test_multiple_line_filters
       end
     end
 
-    def test_line_filter_without_line_runs_all_tests
-      create_test_file :models, 'account'
-
-      run_test_command('test/models/account_test.rb:').tap do |output|
-        assert_match 'AccountTest', output
-      end
-    end
-
     def test_shows_filtered_backtrace_by_default
       create_backtrace_test