Improve GitHub workflow setup

[oalders]

• Add workflow_dispatch to GH workflow triggers
• build and coverage jobs on perl 5.34
• Add 5.34 to GH test matrix
• Ensure test deps are installed in GH workflows

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@bcd54b9). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #263   +/-   ##
=========================================
  Coverage          ?   78.89%           
=========================================
  Files             ?       92           
  Lines             ?     3316           
  Branches          ?      941           
=========================================
  Hits              ?     2616           
  Misses            ?      382           
  Partials          ?      318           

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