[SDK Automation - Python] Automation script doesn't need to install node 18 repeatedly

[raych1]

Node 18 has been installed in the spec PR pipeline and each SDK language automation script should not need to re-install it.

The following is the pipeline log for this spec PR:

01:20:23.663 command 	sh scripts/automation_generate.sh ../azure-sdk-for-python_tmp/generateInput.json ../azure-sdk-for-python_tmp/generateOutput.json
01:20:23.663 info 	Config: {"stderr":{"showInComment":true},"stdout":{"showInComment":"^\\[Autorest\\]"},"envs":[],"exitCode":{"showInComment":true,"result":"error"}}
01:20:33.792 cmdout 	[automation_generate.sh] changed 1 package in 3s
01:20:33.793 cmderr 	[automation_generate.sh]  
01:20:33.793 cmderr 	[automation_generate.sh] npm notice New minor version of npm available! 10.2.4 -> 10.5.0
01:20:33.793 cmderr 	[automation_generate.sh] npm notice Changelog: <[https://github.com/npm/cli/releases/tag/v10.5.0>](https://github.com/npm/cli/releases/tag/v10.5.0%3E)
01:20:33.793 cmderr 	[automation_generate.sh] npm notice Run `npm install -g npm@10.5.0` to update!
01:20:33.794 cmderr 	[automation_generate.sh] npm notice 
01:20:33.850 cmdout 	[automation_generate.sh]   installing : node-v18.19.0
01:20:33.895 cmdout 	[automation_generate.sh]        mkdir : /usr/local/n/versions/node/18.19.0
01:20:33.897 cmdout 	[automation_generate.sh]        fetch : https://nodejs.org/dist/v18.19.0/node-v18.19.0-linux-x64.tar.xz
01:20:35.552 cmdout 	[automation_generate.sh]      copying : node/18.19.0
01:20:37.155 cmdout 	[automation_generate.sh]    installed : v18.19.0 (with npm 10.2.3)

@msyyc

[msyyc]

fixed by Azure/azure-sdk-for-python#35399