getdns: Update to 1.7.3

getdns: Update to 1.7.3

Changelog from upstream (https://github.com/getdnsapi/getdns/releases/tag/v1.7.3):

* 2022-12-22: Version 1.7.3
  * PR getdnsapi/getdns#532: Increase CMake required version 3.5 -> 3.20, because we
    need cmake_path for Absolute paths in pkg-config (See Issue getdnsapi/getdns#517)
    Thanks Gabriel Ganne
  * Updated to Stubby 0.4.3 quickfix release

* 2022-08-19: Version 1.7.2
  * Stubby updated to 0.4.2 quickfix release

* 2022-08-19: Version 1.7.1
  * Always send the `dot` ALPN when using DoT
  * Strengthen version determination for Libidn2 during cmake processing
    (thanks jpbion).
  * Fix for issue in UDP stream selection in case of timeouts.
    Thanks Shikha Sharma
  * Fix using asterisk in ipstr for any address. Thanks uzlonewolf.
  * Issue getdnsapi/stubby#295: rdata not correctly written for validation for
    certain RR type. Also, set default built type to RelWithDebInfo and
    expose CFLAGS via GETDNS_BUILD_CFLAGS define and via
    getdns_context_get_api_information()
  * Issue getdnsapi/getdns#524: Bug fixes from submodules' upstream?
    Thanks Johnnyslee
  * Issue getdnsapi/getdns#517: Allow Absolute path CMAKE_INSTALL_{INCLUDE,LIB}DIR in
    pkg-config files. Thanks Alex Shpilkin
  * Issue getdnsapi/getdns#512: Update README.md to show correct PGP key location.
    Thanks Katze Prior.

Signed-off-by: Aquila Cooper <aquila@cpr.is>