[PR #10285/3ab7a898 backport][stable-11] replace concatenations with f-string in plugins (#10290)

replace concatenations with f-string in plugins (#10285)

* replace concatenations with f-string in plugins

* add changelog frag

(cherry picked from commit 3ab7a898c6)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>

plugins/callback/mail.py

@@ -212,7 +212,8 @@ class CallbackModule(CallbackBase):
         if self.itembody:
             body += self.itembody
         elif result._result.get('failed_when_result') is True:
-            fail_cond = self.indent('failed_when:\n- ' + '\n- '.join(result._task.failed_when))
+            fail_cond_list = '\n- '.join(result._task.failed_when)
+            fail_cond = self.indent(f"failed_when:\n- {fail_cond_list}")
             body += f"due to the following condition:\n\n{fail_cond}\n\n"
         elif result._result.get('msg'):
             body += self.body_blob(result._result['msg'], 'message')