Fix invalid repository URLs in 'Elyra in an air gapped environment' topic

[ptitzler]

In version 3.9.0rc0 some URLs in the Running Elyra in an air gapped environment topic were corrupted by the release script. This PR fixes the problems.

What changes were proposed in this pull request?

s/v3.9.0rc0/main/g

How was this pull request tested?

• Reviewed the output of make docs
  

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[kiersten-stokes]

Good catch!

[lresende]

@ptitzler you need to remove the final / from first URL as it will throw a 400 - invalid request

[ptitzler]

@ptitzler you need to remove the final / from first URL as it will throw a 400 - invalid request

Oops. Thank you. Fixed!