Update 1.6 release notes for v1.6.1

[jakexks]

This clarifies the issues with Java Keystores are now fixed.

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[maelvls]

+++ Running spell check
    content/en/docs/release-notes/release-notes-1.6.md
       30 | er applies as it was fixed in v1.6.1, but will remain here for  
       31 | en't upgraded cert-manager to v1.6.0 from any v1.5 
       31 | rt-manager to v1.6.0 from any v1.5 
       32 |  the latest version, skipping v1.6.0. 

[maelvls]

/lgtm
/approve

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