scripts: west flash with stm32CubeProgrammer error line

Correct the error "F541 f-string is missing placeholders"
when ruuning Flake

Signed-off-by: Francois Ramu <francois.ramu@st.com>
diff --git a/scripts/west_commands/runners/stm32cubeprogrammer.py b/scripts/west_commands/runners/stm32cubeprogrammer.py
index 026e532..b57864a 100644
--- a/scripts/west_commands/runners/stm32cubeprogrammer.py
+++ b/scripts/west_commands/runners/stm32cubeprogrammer.py
@@ -200,7 +200,7 @@
         # flash image and run application
         dl_file = self.cfg.elf_file if self._use_elf else self.cfg.hex_file
         if dl_file is None:
-            raise RuntimeError(f'cannot flash; no download file was specified')
+            raise RuntimeError('cannot flash; no download file was specified')
         elif not os.path.isfile(dl_file):
             raise RuntimeError(f'download file {dl_file} does not exist')
         self.check_call(cmd + ["--download", dl_file, "--start"])