fix missing filename in 'Unable to read keypair file' errors

[mikemaccana]

Fixes #2884

[vercel[bot]]

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[mikemaccana]

Thanks. I did try and make get_keypair() take a path instead originally but read_keypair_file() really wants the trait AsRef<std::path::Path> and WalletPath doesn't implement it. I ended up converting to a string in this most recent update, is there a better way?

read_keypair_file in your editor and fix all of them

Missed that one (originally I skipped it when playing with WalletPath as it wants a string). Got it now.

[mikemaccana]

cargo clippy bits fixed too.