chore: use sha256 in hashing (#3012)

Fix:
https://github.com/googleapis/sdk-platform-java/security/code-scanning/1

Author: JoeWang1127

library_generation/model/library_config.py

@@ -12,7 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-from hashlib import sha1
+from hashlib import sha256
 
 from typing import Optional
 from library_generation.model.gapic_config import GapicConfig
@@ -117,7 +117,7 @@ def __eq__(self, other):
         )
 
     def __hash__(self):
-        m = sha1()
+        m = sha256()
         m.update(
             str(
                 [