[BEAM-11689] (release-2.28.0) Add public.nexus.pentaho.org to offline repositories.

[ibzib]

cherry-pick #13823

R: @chamikaramj

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Post-Commit Tests Status (on master branch)

Lang	SDK	Dataflow	Flink	Samza	Spark	Twister2
Go		---		---		---
Java
Python				---		---
XLang				---		---

Pre-Commit Tests Status (on master branch)

---	Java	Python	Go	Website	Whitespace	Typescript
Non-portable
Portable	---		---	---	---	---

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GitHub Actions Tests Status (on master branch)

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-2.28.0@a946429). Click here to learn what that means.
The diff coverage is n/a.

@@                Coverage Diff                @@
##             release-2.28.0   #13828   +/-   ##
=================================================
  Coverage                  ?   82.76%           
=================================================
  Files                     ?      466           
  Lines                     ?    57557           
  Branches                  ?        0           
=================================================
  Hits                      ?    47636           
  Misses                    ?     9921           
  Partials                  ?        0           

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[chamikaramj]

Thanks. Python failure is due to container "gcr.io/cloud-dataflow/v1beta3/python37-fnapi:2.28.0" not being available yet.

[chamikaramj]

LGTM