Exclude `routers/private/tests` from air (#29949)

Exclude this and reformat the toml option to multiline.

I wasn't able to get `exclude_regex` to work so it would include a
`tests` directory anywhere. I think that option only works on files.

.air.toml

@@ -8,6 +8,15 @@ delay = 1000
 include_ext = ["go", "tmpl"]
 include_file = ["main.go"]
 include_dir = ["cmd", "models", "modules", "options", "routers", "services"]
-exclude_dir = ["modules/git/tests", "services/gitdiff/testdata", "modules/avatar/testdata", "models/fixtures", "models/migrations/fixtures", "modules/migration/file_format_testdata", "modules/avatar/identicon/testdata"]
+exclude_dir = [
+  "models/fixtures",
+  "models/migrations/fixtures",
+  "modules/avatar/identicon/testdata",
+  "modules/avatar/testdata",
+  "modules/git/tests",
+  "modules/migration/file_format_testdata",
+  "routers/private/tests",
+  "services/gitdiff/testdata",
+]
 exclude_regex = ["_test.go$", "_gen.go$"]
 stop_on_error = true