dnscrypt-proxy: update to 2.1.5.

[g4s8]

Testing the changes

• I tested the changes in this PR: YES

Local build testing

• I built this PR locally for my native architecture, (x86_64)
• I built this PR locally for these architectures (if supported. mark crossbuilds):
  • i686
  • aarch64
  • armv7l

The new version 2.1.5 fixes go1.21.0 version support, see changelog:

Version 2.1.5

• dnscrypt-proxy can be compiled with Go 1.21.0+
• Responses to blocked queries now include extended error codes
• Reliability of connections using HTTP/3 has been improved
• New configuration directive: tls_key_log_file. When defined, this
  is the path to a file where TLS secret keys will be written to, so
  that DoH traffic can be locally inspected.

[g4s8]

@Duncaen @cinerea0 this PR should fix a0bae1c

[cinerea0]

I already have an open PR for this: #45595.