ddns-scripts: Add option 'myip=no' to Dynu IPv6 update URL

[dmsza]

Maintainer: @feckert
Compile tested: NanoPI R6S, OpenWrt 24.10.0
Run tested: NanoPI R6S, OpenWrt 24.10.0. Confirmed that after this change only IPv6 is updated in DynuDDNS.

Description:
This forces Dynu script to update only the AAAA entry for IPv6 updates. This prevents Dynu from registering an IPv4 address during IPv6 updates. Without this parameter, routers behind a CGNAT with a public IPv6 address would incorrectly register the CGNAT’s IPv4 address, even when updating IPv6 only.

[dmsza]

Missing "Signed-off-by" added to the commit message, fixing the failed test [Test Formalities / Test Formalities (pull_request)].

Other tests failures are not related to this commit (possibly an issue with the test environment?)

[feckert]

• You have to update the commit Message. The length constrains are 80 character for each line.
• Please fix CI/CD this is mostly an incorrect git config on your System. Your first and last name for your Signed-off-by does have to fit with the settings in your git config.