Allow empty certificate passphrase

[ofalvai]

Checklist

• I've read and followed the Contribution Guidelines
• step.yml and README.md is updated with the changes (if needed)

Version

Requires a PATCH version update

Context

Fixing the same issue as in bitrise-steplib/bitrise-step-manage-ios-code-signing#13

Changes

• Update go-xcode to pull this change: Improve empty passphrase handling bitrise-io/go-xcode#161
• passphrase_list input is no longer a required input. This allows using a single certificate without a passphrase because in this case the input should be empty
• Add E2E test that tests the above by using a single certificate without a passphrase
• (Not visible in the diff, but) I added this certificate to $BITFALL_APPLE_IOS_CERTIFICATE_URL_LIST and $BITFALL_APPLE_IOS_CERTIFICATE_PASSPHRASE_LIST too, checking the case when one of the supplied certificates is without a passphrase
• Update step input description

Investigation details

Decisions