Update nix

[berberman]

• tracy-0.7.7 is available with fix of the build on macOS
• lsp{,types}-1.2, lsp-test-0.14.0 (UPDATE: it seems that nix doesn't update them), and other packages which may have updates can be used with nix

This PR also adds a command gen-hls-changelogs to nix shell, calling GenChangelogs.hs with dependencies resolved by nix -- maintainers who use nix now can invoke this script smoothly.

[pepeiborra]

Nice!

[berberman]

@jneira Looks like skipping CI jobs didn't work properly

[jneira]

i am afraid ./shell.nix does not match actual list of ignored paths

Did not find other workflow-runs to be cancelled
Stop backtracking at commit https://github.com/haskell/haskell-language-server/commit/35db90d6a3e059ceca8bc6bc5c3f2f76ab4b6a98 because 'docs/releases.md,nix/default.nix,shell.nix' are not skippable against paths '' or paths_ignore '**/docs/**,**.md,**/LICENSE,.circleci/**,install/**,nix/**'
Do not skip execution because we did not find a transferable run