Fix issue: unprintable character is rendered when handling comments in j2 (#16287)

Use "{#-" and "-#}" to mark comments in jinja template

Signed-off-by: Stephen Sun <stephens@nvidia.com>

platform/mellanox/mlnx-fw-upgrade.j2

@@ -1,4 +1,4 @@
-{#
+{#-
     Copyright (c) 2020-2023 NVIDIA CORPORATION & AFFILIATES.
     Apache-2.0
 
@@ -13,7 +13,7 @@
     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.
-#}
+-#}
 #!/bin/bash
 
 declare -r SCRIPT_NAME="$(basename "$0")"