ci: improve pre-commit error reporting

In the CI, enable --show-diff-on-failure, to show the generated diff by the hooks on errors.

In pre-commit, enable --show-fixes in ruff's linter to summarize the applied fixes by files.

✗ pre-commit run --all-files --show-diff-on-failure
ruff.....................................................................Failed
- hook id: ruff
- files were modified by this hook

Fixed 1 error:
- cerbero/main.py:
    1 × F401 (unused-import)

Found 1 error (1 fixed, 0 remaining).

ruff-format..............................................................Passed
pre-commit hook(s) made changes.
If you are seeing this message in CI, reproduce locally with: `pre-commit run --all-files`.
To run `pre-commit` as part of git workflow, use `pre-commit install`.
All changes made by hooks:
diff --git a/cerbero/main.py b/cerbero/main.py
index d72151d4..e79c1b14 100644
--- a/cerbero/main.py
+++ b/cerbero/main.py
@@ -16,7 +16,6 @@
 # Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 # Boston, MA 02111-1307, USA.
 
-from cerbero import hacks  # noqa: F401
 
 import argparse
 import sys