Version Bump to v20.5

Summary: Version bump 20.4->20.5

Test Plan:

make check
bitcoind --version
bitcoin-cli --version
bitcoin-tx -h
bitcoin-qt --version

ninja check
bitcoind --version
bitcoin-cli --version
bitcoin-tx -h
bitcoin-qt --version

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4246