### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

I prefer not to use the real regions when doing tests or local stuff to make sure that if it accidentally picks up real credentials, it won't actually create or interact with resources in AWS. This used to work find in localstack - I even dug through the code to find that there is an option in the `RegionStore` to disable validation of the region string. At some point, you removed any way to disable that validation though, which means it just fails all requests using a custom region.

### 🧑‍💻 Implementation

There's already a flag that is passed to the account and region store constructors to disable validation. Seems like an environment variable or configuration flag to disable validation could be propagated.

### Anything else?

_No response_
"""
        Clear all store data.
        This only deletes the data held in the stores. All instantiated stores
        are retained. This includes data shared by all stores in this account
        and marked by the CrossRegionAttribute descriptor.
        Data marked by CrossAccountAttribute descriptor is only cleared when
        `_reset_universal` is set. Note that this escapes the logical boundary of
        the account associated with this RegionBundle and affects *all* accounts.
        Hence this argument is not intended for public use and is only used when
        invoking this method from AccountRegionBundle.
        """
        
        for store_inst in self.values():
            attrs = list(store_inst.__dict__.keys())
            for attr in attrs:
                
                if attr == "_global":
                    store_inst._global.clear()
                if attr == "_universal" and _reset_universal:
                    store_inst._universal.clear()
                
                elif attr.startswith(LOCAL_ATTR_PREFIX):
                    delattr(store_inst, attr)
        self._global.clear()
        with self.lock:
            self.clear()
class AccountRegionBundle(dict, Generic[BaseStoreType]):