Change rust-version in Cargo.toml to comply with MSRV

[sarutak]

Which issue does this PR close?

Closes #7106

Rationale for this change

As I explained in #7106, we can't build datafusion with Rust 1.64 which is specified in Cargo.toml.

What changes are included in this PR?

Changed rust-version in Cargo.toml. I decided the version as reported by cargo msrv.

Are these changes tested?

Confirmed I can build with Rust 1.70.

Are there any user-facing changes?

No.

[alamb]

Thank you very much @sarutak

There was a similar issue apache/arrow-rs#4487 on arrow-rs a few weeks ago and part of that PR was to add a CI check to ensure the msrv was valid.

Are you willing to try and add such a check for DataFusion so the toml file doesn't drift out of sync again?

[sarutak]

@alamb

There was a similar issue apache/arrow-rs#4487 on arrow-rs a few weeks ago and part of that PR was to add a CI check to ensure the msrv was valid.

Are you willing to try and add such a check for DataFusion so the toml file doesn't drift out of sync again?

Thank you for letting me know!
It's nice to have, and I'll try it.