Fix F541: replace f-strings with no placeholders in lightning tests

[nikunjkumar05]

Changelog-None

About PR

This PR fixes flake8 F541 (f-strings missing placeholders) by replacing f-strings that contain no placeholders with plain strings in the lightning test files. These were lint errors only but reduce noise and avoid confusion.

Why

F541 indicates an f-string with no {} placeholders — likely a typo. Replacing with a plain string removes the lint error and clarifies intent.

How to Test

flake8 lightning/tests || true

Checklist

• Changelog-None
• Tests have been added or modified to reflect the changes.
• Documentation has been reviewed and updated as needed.
• Related issues have been listed and linked, including any that this PR closes.
• Important All PRs must consider how to reverse any persistent changes for tools/lightning-downgrade

[nikunjkumar05]

@rustyrussell @daywalker90 @Lagrang3 please review my PR
thank you

[daywalker90]

You need to add "Changelog-None" to the PR or commit message. Otherwise looks good to me.

[nikunjkumar05]

ok sir

[nikunjkumar05]

@rustyrussell @daywalker90 @Lagrang3
Thank you for review
changes addressed sir please review the PR

[madelinevibes]

@nikunjkumar05 thanks for your contribution. You haven't replaced all of the possible F541 (f-strings missing placeholders). There are a lot of different files that have this dev string. We will holding off reviewing further until the PR has all of the replacements required.

[nikunjkumar05]

Ok @madelinevibes thank you for review I will fix it shortly

[madelinevibes]

great that you've had a review but now @nikunjkumar05 you need to update so the PR passes CI. Thanks!

[ShahanaFarooqui]

Hi @nikunjkumar05, I am not approving the workflow to run just yet. Since the last commit is guaranteed to fail CI, running it now would just waste build minutes. Let's get all those fixes in first.

[madelinevibes]

Please rebase (not merge!) and squash everything into one clean commit when you're done. It's quite messy right now. Thanks!

[nikunjkumar05]

I think ready for review