Merge bitcoin/bitcoin#31417: test: Avoid F541 (f-string without any placeholders)

fae76393bd test: Avoid F541 (f-string without any placeholders) (MarcoFalke)

Pull request description:

  An extra `f` string-prefix is mostly harmless, but could be confusing or hint to a mistake where a format argument was forgotten.

  Try to avoid the confusion and mistakes by applying the `F541` linter rule.

ACKs for top commit:
  lucasbalieiro:
    **Tested ACK** [fae7639](https://github.com/bitcoin/bitcoin/pull/31417/commits/fae76393bdbf867176e65447799d6ee3d3567b18)
  danielabrozzoni:
    ACK fae76393bd
  tdb3:
    Code review ACK fae76393bd

Tree-SHA512: 4992a74fcf0c19b32e4d95f7333e087b4269b5c5259c556789fb86721617db81c7a4fe210ae136c92824976f07f71ad0f374655e7008b1967c02c73324862d9a

test/lint/test_runner/src/main.rs

@@ -226,6 +226,7 @@ fn lint_py_lint() -> LintResult {
             "F405", // foo_function may be undefined, or defined from star imports: bar_module
             "F406", // "from module import *" only allowed at module level
             "F407", // an undefined __future__ feature name was imported
+            "F541", // f-string without any placeholders
             "F601", // dictionary key name repeated with different values
             "F602", // dictionary key variable name repeated with different values
             "F621", // too many expressions in an assignment with star-unpacking