ci: use ubuntu docker container to build linux releases

[koppchen]

Switch back to Ubuntu 18.04 for building linux releases. This allows for running these on older systems that do not provide GLIBC_2.29.

fix #1828

[koppchen]

Feel free to change this or use another solution. I've only tested the linux-x64 version

Tested on an Ubuntu 18:04 vagrant box

vagrant@ubuntu-bionic:/vagrant$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 18.04.6 LTS
Release:        18.04
Codename:       bionic

Test with the 3.6.6 release (which gives the "GLIBC_2.29' not found" error)

vagrant@ubuntu-bionic:/vagrant$ ./lua-language-server-3.6.6-linux-x64/bin/lua-language-server
./lua-language-server-3.6.6-linux-x64/bin/lua-language-server: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.29' not found (required by ./lua-language-server-3.6.6-linux-x64/bin/lua-language-server)
./lua-language-server-3.6.6-linux-x64/bin/lua-language-server: /lib/x86_64-linux-gnu/libm.so.6: version `GLIBC_2.29' not found (required by ./lua-language-server-3.6.6-linux-x64/bin/lua-language-server)

Test with the linux-x64 binary generated with this change.

vagrant@ubuntu-bionic:/vagrant$ ./lua-language-server-88699be-linux-x64/bin/lua-language-server
Content-Length: 120

{"jsonrpc":"2.0","method":"$/status/report","params":{"text":"😺Lua","tooltip":"Cached files: 0/0\nMemory usage: 2M"}}

[sumneko]

Thank you!

[sumneko]

Could you please open a similar PR to https://github.com/sumneko/vscode-lua/blob/master/.github/workflows/build.yml ?

[koppchen]

Sure, no problem, I'll look into it later today.
Thank you!