Fix track_memory_usage on poetry-core 1.3.x installations

The same kind of problem as discussed in #14085:

1. we defined an extra with an underscore
2. we look it up at runtime with an underscore
3. but poetry-core 1.3.x. installs it with a dash, causing (2) to fail.

Fix by using a dash everywhere.

pyproject.toml

@@ -227,7 +227,7 @@ jwt = ["authlib"]
 # (if it is not installed, we fall back to slow code.)
 redis = ["txredisapi", "hiredis"]
 # Required to use experimental `caches.track_memory_usage` config option.
-cache_memory = ["pympler"]
+cache-memory = ["pympler"]
 test = ["parameterized", "idna"]
 
 # The duplication here is awful. I hate hate hate hate hate it. However, for now I want
@@ -258,7 +258,7 @@ all = [
     "jaeger-client", "opentracing",
     # redis
     "txredisapi", "hiredis",
-    # cache_memory
+    # cache-memory
     "pympler",
     # omitted:
     #   - test: it's useful to have this separate from dev deps in the olddeps job

synapse/config/cache.py

@@ -159,7 +159,7 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
 
         self.track_memory_usage = cache_config.get("track_memory_usage", False)
         if self.track_memory_usage:
-            check_requirements("cache_memory")
+            check_requirements("cache-memory")
 
         expire_caches = cache_config.get("expire_caches", True)
         cache_entry_ttl = cache_config.get("cache_entry_ttl", "30m")