Update type annotations for compatiblity with prometheus_client 0.14 (#12389)

Principally, `prometheus_client.REGISTRY.register` now requires its argument to
extend `prometheus_client.Collector`.

Additionally, `Gauge.set` is now annotated so that passing `Optional[int]`
causes an error.

1 files changed, 2 insertions, 1 deletions

diff --git a/synapse/metrics/background_process_metrics.py b/synapse/metrics/background_process_metrics.py

index 53c508af91..f61396bb79 100644
--- a/synapse/metrics/background_process_metrics.py
+++ b/synapse/metrics/background_process_metrics.py
@@ -46,6 +46,7 @@ from synapse.logging.opentracing import (
     noop_context_manager,
     start_active_span,
 )
+from synapse.metrics._types import Collector
 
 if TYPE_CHECKING:
     import resource
@@ -127,7 +128,7 @@ _background_processes_active_since_last_scrape: "Set[_BackgroundProcess]" = set(
 _bg_metrics_lock = threading.Lock()
 
 
-class _Collector:
+class _Collector(Collector):
     """A custom metrics collector for the background process metrics.
 
     Ensures that all of the metrics are up-to-date with any in-flight processes