chore: update librarian version to v0.49.0 (#18779)

Update librarian version to v0.49.0.

## Debug Info
### System Details
- Python version: Python 3.13.15
- OS: Linux 7.1.6-1rodete1-amd64 x86_64
- Librarian version: v0.49.0

### Commands Executed
- `python3 -m venv "$VENV_DIR" && source "$VENV_DIR/bin/activate"`
- `pip install --upgrade pip`
- `go run github.com/googleapis/librarian/cmd/librarian@latest update
version`
- `go run github.com/googleapis/librarian/cmd/librarian@v0.49.0 tidy`
- `go run github.com/googleapis/librarian/cmd/librarian@v0.49.0 install`
- `go run github.com/googleapis/librarian/cmd/librarian@v0.49.0 generate
--all`
- `git add .`
- `git commit -m "chore: update librarian version to v0.49.0"`

Author: suztomo

librarian.yaml

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 language: python
-version: v0.48.0
+version: v0.49.0
 repo: googleapis/google-cloud-python
 sources:
   googleapis: