Release a version built with supported Go version

[stefanb]

Currently used Go 1.18 and 1.19 are not supported anymore.

After #300 it is now buildable with both Go 1.21 and upcoming 1.22 (now at 1.22rc1)

Please

• update github workflows and Dockerfiles to use supported stable Go version (currently 1.21)
• tag a release

See also:

• go 1.22.0 Homebrew/homebrew-core#157782
• go 1.21.7 Homebrew/homebrew-core#161976
• go 1.24.0, go@1.23 1.23.6 (new formula) Homebrew/homebrew-core#201070

[prusnak]

Addressed in #308 but I am not sure when we will cut a new release with the changes.

The changes need to be properly tested with real devices before releasing new version.