postgres tests: Reenable silent-connection-drop workflow

Noticed in https://buildkite.com/materialize/nightly/builds/14327#019ae19e-2845-4d99-b6d3-c02ed5e41c21

Since MaterializeInc/database-issues#8447 has
been closed by #34280

Author: def-

test/pg-cdc-old-syntax/mzcompose.py

@@ -383,10 +383,6 @@ def process(name: str) -> None:
         if name in ("default", "migration", "migration-multi-version-upgrade"):
             return
 
-        # TODO: Flaky, reenable when database-issues#8447 is fixed
-        if name == "silent-connection-drop":
-            return
-
         c.kill("postgres")
         c.rm("postgres")
         c.kill("materialized")

test/pg-cdc/mzcompose.py

@@ -424,10 +424,6 @@ def process(name: str) -> None:
         if name in ("default", "large-scale"):
             return
 
-        # TODO: Flaky, reenable when database-issues#8447 is fixed
-        if name == "silent-connection-drop":
-            return
-
         c.kill("postgres")
         c.rm("postgres")
         c.kill("materialized")