App tests should exercise `--reload`

[gadenbuie]

The issue in #1188 reveals that our tests don't run any apps with --reload enabled. (Well, I haven't explicitly checked this statement, but I'm assuming that's why #1183 didn't fail test checks.)

Since many users will run Shiny apps with --reload enabled -- because this is the default workflow for the vscode extension -- we should make sure that our tests use this flag in at least some cases.

[jquerypageleave]

For anyone wanting to have it not reload automatically (for whatever reasons, long calculations, saving files in the directory, whatever), have a look at https://stackoverflow.com/a/78260214/1231450