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, 3 insertions, 1 deletions

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

index f38f798313..a2c6e6842d 100644
--- a/synapse/metrics/_reactor_metrics.py
+++ b/synapse/metrics/_reactor_metrics.py
@@ -21,6 +21,8 @@ from prometheus_client.core import REGISTRY, GaugeMetricFamily
 
 from twisted.internet import reactor
 
+from synapse.metrics._types import Collector
+
 #
 # Twisted reactor metrics
 #
@@ -54,7 +56,7 @@ class EpollWrapper:
         return getattr(self._poller, item)
 
 
-class ReactorLastSeenMetric:
+class ReactorLastSeenMetric(Collector):
     def __init__(self, epoll_wrapper: EpollWrapper):
         self._epoll_wrapper = epoll_wrapper