Update __version__ on __init__.py to 0.7.0 (huggingface#2017)

There was a new release of the python client with version upped to 0.7.0
on pip and on the pyproject.toml, but it wasn't changed on the
__init__.py so when one does:

```python
import text_generation
print(text_generation.__version__)
```

It still outputs "0.6.0"

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Fixes # (issue)

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clients/python/text_generation/__init__.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-__version__ = "0.6.0"
+__version__ = "0.7.0"
 
 DEPRECATION_WARNING = (
     "`text_generation` clients are deprecated and will be removed in the near future. "