MLBEDSW-3367 Update pre-commit flake8 version

Update the version of flake8 used in pre-commit to facilitate
adding mypy to pre-commit.

Signed-off-by: Jonas Ohlsson <jonas.ohlsson@arm.com>
Change-Id: I457dec87b77487ca6f14ff4a679c4cc927b272b0
diff --git a/ethosu/vela/scheduler.py b/ethosu/vela/scheduler.py
index 6b08459..3ef0d7f 100644
--- a/ethosu/vela/scheduler.py
+++ b/ethosu/vela/scheduler.py
@@ -1099,7 +1099,7 @@
             )
             print(f"\t\tSRAM Used: {mem_usage} bytes")
 
-        print(f"\tCascades:")
+        print("\tCascades:")
         for i, cascade in enumerate(schedule.cascades.values()):
             print(f"\t\t{i}: {cascade.start} -> {cascade.end}, size: {cascade.mem_usage}")