Fix source code formatting in ErrorKind::details()

[katrinafyi]

Fixes #1992. Doesn't change anything aside from formatting.

It looks like rustfmt gives up on a function if it has strings which exceed the max_width, because rustfmt doesn't make any changes to string literals.

After some long strings are manually broken up, rustfmt can format the rest of the function.

Example of manual change, old:

            ErrorKind::MissingGitHubToken => Some(
                "GitHub token required. Use --github-token flag or GITHUB_TOKEN environment variable".to_string()
            ),

new:

            ErrorKind::MissingGitHubToken => Some(format!(
                "GitHub token required. {}",
                "Use --github-token flag or GITHUB_TOKEN environment variable",
            )),

Unfortunately, this PR doesn't do anything to prevent this happening again. Some options I looked into:

• The rustfmt options error_on_line_overflow and error_on_unformatted seemed promising. However, I tried both and they do not report the long strings as problems, but they do report different unrelated errors across the codebase.
• Enable rustfmt option format_strings. Does fix the problem, but sometimes introduces \ inside string literals. Also, the option is unstable and has some known bugs. Could be chosen as a trade-off.

[thomas-zahner]

Thank you! I didn't know about this limitation until now, but I also remember being confused why rustfmt didn't work int that section and thought it was an issue on my side. (blaming my IDE probably)

format_strings sounds promising, but I guess we need to wait until it's stabilised. I really wouldn't use it while unstable.

[mre]

Nice catch. It looks much better now.