Update rust driver rev in Cargo.toml

[Gor027]

Imported scylla-rust-driver by commit hash 9dc6f4871f2. This will include all pre-execution-profile changes in the Rust driver and will resolve the following conflicts:

• Removed BadQuery::ValueLenMismatch error, as it was also removed from the Rust driver to allow removing len from BatchValues.

• Resolved conflicts after custom authentication feature was added to the Rust driver.

It was requested by @wprzytula and it aims to make the addition of execution profiles easier.

Pre-review checklist

• [x] I have split my patch into logically separate commits.
• [x] All commit messages clearly explain what they change and why.
• [x] PR description sums up the changes and reasons why they should be introduced.
• [ ] I have enabled appropriate tests in .github/workflows/build.yml in gtest_filter.
• [ ] I have enabled appropriate tests in .github/workflows/cassandra.yml in gtest_filter.

[Gor027]

This PR is dependent upon the fix https://github.com/scylladb/cpp-rust-driver/pull/104 to pass the CI successfully.