Alpine Linux just pushed icu-76 to the main repository of Alpine Linux edge, and all related packages are being rebuild (e.g. firefox, chromium, plasma-desktop and many many more). Since icu-76 is already pushed to the main repository and the community and testing repositories aren't built and uploaded yet, these repositories are broken until all rebuilds are completed.
You can follow the progress on https://build.alpinelinux.org/. If the activity of the builder is "idle", the builder finished building and everything should work as expected.
There are a few packages failing to rebuild. Help is appreciated in resolving these build failures. Feel free to get in touch in #alpine-devel on OFTC or #_oftc_#alpine-devel:matrix.org on Matrix.