Switch over to the toolchain swift-format from building it in the CI script

### Description

Now that Linux Swift toolchains have swift-format, we can speed up our CI.

Note that we can only do this for nightly Swift versions for now.

### Additional information

_No response_

Start by locating the CI script that builds swift-format and the configuration for nightly Swift toolchains. Done means nightly Linux toolchains use their provided swift-format while other supported Swift versions retain the existing behavior, with CI completing successfully.

Written by the indexing model from the issue text.