Turn provider's import warnings into debug logs (#14903)

When only some providers are installed, cross-dependencies between
the providers might cause import erors. Those import errors are
repeated in webserver as it is reloaded every 30 seconds.

Since "only some providers" case is valid, it should not generate
warrnings if it is an ImportError. Those warnings are now
turned into debug messages.

Fixes: #14286

Author: potiuk

airflow/providers_manager.py

@@ -280,28 +280,23 @@ def _add_hook(self, hook_class_name: str, provider_package: str) -> None:
                 if field_behaviours:
                     self._add_customized_fields(provider_package, hook_class, field_behaviours)
 
+        except ImportError as e:  # noqa pylint: disable=broad-except
+            # When there is an ImportError we turn it into debug warnings as this is
+            # an expected case when only some providers are installed
+            log.debug(
+                "Exception when importing '%s' from '%s' package: %s",
+                hook_class_name,
+                provider_package,
+                e,
+            )
+            return
         except Exception as e:  # noqa pylint: disable=broad-except
-            if os.environ.get("AIRFLOW_INSTALLATION_METHOD") != ".":
-                # print providers manager warning when airflow is not installed from sources in the
-                # production image
-                log.warning(
-                    "Exception when importing '%s' from '%s' package: %s",
-                    hook_class_name,
-                    provider_package,
-                    e,
-                )
-            else:
-                # This is special case - when airflow is installed from sources in production
-                # image, AIRFLOW_INSTALLATION_METHOD is set to ".". In this case we know that there
-                # Will be some warnings generated by ProviderManager, when it tries to import providers
-                # With missing dependencies, therefore we are turning such warnings into debug message
-                # so that we do not pollute logs.
-                log.debug(
-                    "Exception when importing '%s' from '%s' package: %s",
-                    hook_class_name,
-                    provider_package,
-                    e,
-                )
+            log.warning(
+                "Exception when importing '%s' from '%s' package: %s",
+                hook_class_name,
+                provider_package,
+                e,
+            )
             return
 
         conn_type: str = self._get_attr(hook_class, 'conn_type')