fix: add private tag for nx for o3r-training/showcase-sdk package #12932

Job	Run time
yarn_lock_check	1m 38s
build	3m 48s
version	34s
checks / lint	1m 31s
checks / markdown-link-check	52s
checks / test (ubuntu-latest)	1m 50s
checks / test (windows-latest)	3m 3s
documentation-pr	0s
documentation-main	0s
e2e-tests / e2e-tests	3m 33s
it-tests / prepare-verdaccio	2m 46s
it-tests / it-tests (ubuntu-latest, yarn, o3r-project-with-app)	1m 51s
it-tests / it-tests (ubuntu-latest, npm, o3r-project-with-app)	1m 58s
it-tests / it-tests (windows-latest, yarn, o3r-project-with-app)	4m 38s
it-tests / it-tests (windows-latest, npm, o3r-project-with-app)	4m 36s
publish-packages	0s
	32m 38s

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