cabal install currently uses `tls-2.x` which seems to have issue with Pinboard

[cho-m]

I was recently cabal v2-install-ing this project to uplift various GHC versions in Homebrew and noticed a sample test was failing on newly built binary with:

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pnbackup: Error while communicating with the Pinboard server: InternalException (HandshakeFailed (Error_Protocol "peer does not support Extended Main Secret" HandshakeFailure))

From quick glance, it looks like tls >= 2 introduced a stricter requirement on Extended Main Secret support based on similar issue reported in git-annex - https://git-annex.branchable.com/bugs/tls__58___peer_does_not_support_Extended_Main_Secret/

Building with --constraint=tls<2 seems to avoid this issue. Not sure if there is a better way to handle this.