Sort __all__ list alphabetically (#230)

Make ruff happy. It updated automated on the CI and now it's failing
because this list wasn't sorted. Sort it to pass the CI.

src/appsignal/__init__.py

@@ -27,26 +27,26 @@
 
 __all__ = [
     "Appsignal",
+    "Heartbeat",
+    "add_distribution_value",
+    "check_in",
+    "heartbeat",
+    "increment_counter",
+    "send_error",
+    "send_error_with_context",
     "set_body",
-    "set_sql_body",
     "set_category",
     "set_custom_data",
+    "set_error",
+    "set_gauge",
     "set_header",
     "set_name",
     "set_namespace",
     "set_params",
     "set_root_name",
     "set_session_data",
+    "set_sql_body",
     "set_tag",
-    "set_error",
-    "send_error",
-    "send_error_with_context",
-    "increment_counter",
-    "set_gauge",
-    "add_distribution_value",
-    "Heartbeat",
-    "heartbeat",
-    "check_in",
     "start",
 ]