### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

* Create any table with any records
* Do a TransactGetItems on the table
* Localstack returns 
```
ResourceNotFoundException: Cannot do operations on a non-existent table
```

### Expected Behavior

TransactGetItems should succeed.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

```
docker-compose up
```

`docker-compose.yml`
```
version: '3'

services:
  localstack:
    image: localstack/localstack
    environment:
      - DEFAULT_REGION=eu-west-2
      - SERVICES=dynamodb
      - DOCKER_HOST=unix:///var/run/docker.sock
    ports:
      - 4566:4566
```

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

```
#! /bin/bash
aws --endpoint-url=http://localhost:4566 dynamodb create-table --attribute-definitions AttributeName=forumId,AttributeType=S --table-name forum --key-schema AttributeName=forumId,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 > /dev/null
aws --endpoint-url=http://localhost:4566 dynamodb put-item --table-name forum --item '{"forumId": {"S": "forum001"}, "data": {"S": "helloworld"}}' > /dev/null
aws --endpoint-url=http://localhost:4566 dynamodb get-item --table-name forum --key '{"forumId": {"S": "forum001"}}' > /dev/null
# This one fails
aws --endpoint-url=http://localhost:4566 dynamodb transact-get-items --transact-items '[{"Get": {"Key":{"forumId": {"S": "forum001"}}, "TableName": "forum"}}]' > /dev/null
```


### Environment

```markdown
- OS: MacOS 10.15.7
- LocalStack: latest, digest 843db39ff1df83fd537e15b30e39d6fb8c3590efd6bf3f6f96b1734418fbd19f
```


### Anything else?

This works in `localstack/localstack:0.14.1`
import copy
import json
import logging
import random
import re
import time
import traceback
from typing import Dict, List
import requests
import werkzeug
from localstack import config, constants
from localstack.aws.api import (
    CommonServiceException,
    RequestContext,
    ServiceRequest,
    ServiceResponse,
    handler,
)
from localstack.aws.api.dynamodb import (
    BatchGetItemOutput,
    BatchGetRequestMap,
    BatchWriteItemInput,
    BatchWriteItemOutput,
    BillingMode,
    CreateGlobalTableOutput,
    CreateTableInput,
    CreateTableOutput,
    DeleteItemInput,
    DeleteItemOutput,
    DeleteTableOutput,