bump proc-macro2

[salaheldinsoliman]

What

1- Bump proc-macro2 crate in soroban-builtin-sdk-macros and soroban-env-macros
2- add Cargo.lock to .gitignore

Why

A version conflict is happening while building solang, after adding soroban-env-host as a dependancy:
error: failed to select a version for proc-macro2.
... required by package soroban-builtin-sdk-macros v20.2.2
... which satisfies dependency soroban-builtin-sdk-macros = "=20.2.2" of package soroban-env-host v20.2.2
... which satisfies dependency soroban-env-host = "^20.2.2" of package solang v0.3.3
versions that meet the requirements =1.0.69 are: 1.0.69

all possible versions conflict with previously selected packages.

previously selected package proc-macro2 v1.0.78
... which satisfies dependency proc-macro2 = "^1.0.78" of package parse-display-derive v0.9.0
... which satisfies dependency parse-display-derive = "=0.9.0" of package parse-display v0.9.0
... which satisfies dependency parse-display = "^0.9" of package solang v0.3.3

failed to select a version for proc-macro2 which could resolve this conflict

[leighmcculloch]

One request inline.

@graydon I think this is a good example of how pinning deps is going to play out. This won't be the last time that or pinning creates a conflict for embedders.

[leighmcculloch]

One more ask.

[leighmcculloch]

Thanks, this shouldn't have been in here in the first place. 👍🏻

[leighmcculloch]

I misread this diff, I thought it was removing Cargo.lock, but on relook I see it is adding it. We don't want the Cargo.lock file to be excluded from git, for the reasons described here: #1351 (comment)

[leighmcculloch]

Can you change this back to .69 since it isn't necessary for this to select the newer version inside this repo?

[salaheldinsoliman]

Shouldn't I remove the whole file instead?

[leighmcculloch]

There shouldn't be any changes to the lock file, yup.