Ease C++ version requirements in order to support RNP packaging

[maxirmx]

This chane is required in order to suppor sexp inclusion too rnp as source code as discussed at rnpgp/rnp#2004

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (ec6bcc6) 99.70% compared to head (abbe7f4) 99.70%.

❗ Current head abbe7f4 differs from pull request most recent head a805612. Consider uploading reports for the commit a805612 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #23   +/-   ##
=======================================
  Coverage   99.70%   99.70%           
=======================================
  Files           9        9           
  Lines         668      668           
=======================================
  Hits          666      666           
  Misses          2        2           

Impacted Files	Coverage Δ
src/sexp-output.cpp	100.00% <ø> (ø)
include/sexp/sexp.h	100.00% <100.00%> (ø)
src/sexp-input.cpp	100.00% <100.00%> (ø)
src/sexp-object.cpp	98.55% <100.00%> (ø)

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