tests: speed up integration test runs

While running a command from the integration tests, invoke `.result` to
trigger a save of the result set, but don't call `.format!` to avoid
(re)generating the HTML output with every run. The final output will
still be written once the main unit test run completes.

This significantly speeds up the integration tests, that take about 1/3
less time to complete when not generating the intermediate output.

Closes Homebrew/homebrew#48280.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Library/Homebrew/test/.simplecov

@@ -18,7 +18,7 @@ if ENV["HOMEBREW_INTEGRATION_TEST"]
   SimpleCov.at_exit do
     exit_code = $!.nil? ? 0 : $!.status
     $stdout.reopen("/dev/null")
-    SimpleCov.result.format!
+    SimpleCov.result # Just save result, but don't write formatted output.
     exit! exit_code
   end
 end