Klayout should only build release versions only not main

[atorkmabrains]

@proppy It's preferred to use the release versions only of klayout for builds and not to build the main branch:

https://github.com/KLayout/klayout/tags

[proppy]

@atorkmabrains for conda-eda we usually want to be able track, build and package the latest version of tools (even if they have not yet released a formal version).

#193 has some discussions about using conda-forge instead for more "stable" released version of the tools.

but we could also have stable version also packaged in conda-eda (they should conflict because the version/git hash will be different).

maybe @mithro @PiotrZierhoffer @ajelinski have some thoughs around this?

[atorkmabrains]

Having a "stable" branch of the conda environment would be really helpful.