The TypeDecorator.cache_ok class-level flag indicates if this custom
TypeDecorator is safe to be used as part of a cache key. This flag defaults to
None which will initially generate a warning when the SQL compiler attempts to
generate a cache key for a statement that uses this type. If the TypeDecorator
is not guaranteed to produce the same bind/result behavior and SQL generation
every time, this flag should be set to False; otherwise if the class produces
the same behavior each time, it may be set to True. See TypeDecorator.cache_ok
for further notes on how this works.

As I don't know if those can be safely cached, just disable the warning.

Index: mailman-3.3.5/src/mailman/database/types.py
===================================================================
--- mailman-3.3.5.orig/src/mailman/database/types.py	2021-09-06 02:19:59.000000000 +0200
+++ mailman-3.3.5/src/mailman/database/types.py	2022-06-23 08:57:19.527825754 +0200
@@ -34,6 +34,7 @@ class Enum(TypeDecorator):
     converts it on-the-fly.
     """
     impl = Integer
+    cache_ok = False
 
     def __init__(self, enum, *args, **kw):
         super().__init__(*args, **kw)
@@ -59,6 +60,7 @@ class UUID(TypeDecorator):
 
     """
     impl = CHAR
+    cache_ok = False
 
     def load_dialect_impl(self, dialect):
         if dialect.name == 'postgresql':
@@ -97,6 +99,7 @@ class SAUnicode(TypeDecorator):
     column needs to be indexed, otherwise use SAUnicode4Byte.
     """
     impl = Unicode
+    cache_ok = False
 
 
 @compiles(SAUnicode)
@@ -120,6 +123,7 @@ class SAUnicode4Byte(TypeDecorator):
     type and it can still be used if needed in the codebase.
     """
     impl = Unicode
+    cache_ok = False
 
 
 @compiles(SAUnicode4Byte)
@@ -140,6 +144,7 @@ class SAUnicodeLarge(TypeDecorator):
     This is double size of SAUnicode defined above.
     """
     impl = Unicode
+    cache_ok = False
 
 
 @compiles(SAUnicodeLarge, 'mysql')
@@ -166,6 +171,7 @@ class SAUnicodeXL(TypeDecorator):
     See https://docs.sqlalchemy.org/en/latest/dialects/mysql.html#index-length
     """
     impl = Unicode
+    cache_ok = False
 
 
 @compiles(SAUnicodeXL, 'mysql')
@@ -187,6 +193,7 @@ class SAText(TypeDecorator):
     case of other dialects defaults to the Text type.
     """
     impl = Text
+    cache_ok = False
 
 
 @compiles(SAText)