chore(cloud-assembly-schema): update descriptions for networkMode (#18905)

A recent PR, #18114, updated the cloud assembly schema, but parts of the descriptions were missing. Re-running `yarn update-schema` to get them back in sync. I am skipping actually bumping the version of the cloud assembly schema here, because the API is not changing. 


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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: madeline-k

packages/@aws-cdk/cloud-assembly-schema/schema/assets.schema.json

@@ -156,7 +156,7 @@
                     }
                 },
                 "networkMode": {
-                    "description": "Networking mode for the RUN commands during build. _Requires Docker Engine API v1.25+_. (Default - no networking mode specified)",
+                    "description": "Networking mode for the RUN commands during build. _Requires Docker Engine API v1.25+_.\n\nSpecify this property to build images on a specific networking mode. (Default - no networking mode specified)",
                     "type": "string"
                 }
             }
@@ -193,4 +193,4 @@
         }
     },
     "$schema": "http://json-schema.org/draft-07/schema#"
-}
+}

packages/@aws-cdk/cloud-assembly-schema/schema/cloud-assembly.schema.json

@@ -227,7 +227,7 @@
                     "type": "string"
                 },
                 "networkMode": {
-                    "description": "Networking mode for the RUN commands during build. _Requires Docker Engine API v1.25+_. (Default - no networking mode specified)",
+                    "description": "Networking mode for the RUN commands during build. (Default - no networking mode specified)",
                     "type": "string"
                 },
                 "id": {
@@ -874,4 +874,4 @@
         }
     },
     "$schema": "http://json-schema.org/draft-07/schema#"
-}
+}