Replace deprecated openpgp library

[umbynos]

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• The PR has no duplicates (please search among the Pull Requests
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• The PR follows
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• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)
• configuration.schema.json updated if new parameters are added.

What kind of change does this PR introduce?

Dependency replace

What is the current behavior?

The openpgp library we were using has been marked as deprecated (see golang/go#44226)

What is the new behavior?

Replace it with a maintaned one

Does this PR introduce a breaking change, and is titled accordingly?

no

Other information

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (dde3064) 63.04% compared to head (cf9fa1a) 63.04%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2333   +/-   ##
=======================================
  Coverage   63.04%   63.04%           
=======================================
  Files         201      201           
  Lines       19260    19260           
=======================================
  Hits        12142    12142           
  Misses       6065     6065           
  Partials     1053     1053           

Flag	Coverage Δ
unit	63.04% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
arduino/security/signatures.go	65.51% <100.00%> (ø)

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