patch 9.0.1234: the code style has to be checked manually

Problem:    The code style has to be checked manually.
Solution:   Add basic code style checks in a test.  Fix or avoid uncovered
            problems.
diff --git a/src/if_python3.c b/src/if_python3.c
index 270e1a9..240b88f 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -1505,7 +1505,8 @@
     {
 	long _idx = PyLong_AsLong(idx);
 	return BufferItem((BufferObject *)(self), _idx);
-    } else if (PySlice_Check(idx))
+    }
+    else if (PySlice_Check(idx))
     {
 	Py_ssize_t start, stop, step, slicelen;
 
@@ -1539,7 +1540,8 @@
 	return RBAsItem((BufferObject *)(self), n, val, 1,
 		    (Py_ssize_t)((BufferObject *)(self))->buf->b_ml.ml_line_count,
 		    NULL);
-    } else if (PySlice_Check(idx))
+    }
+    else if (PySlice_Check(idx))
     {
 	Py_ssize_t start, stop, step, slicelen;
 
@@ -1623,7 +1625,8 @@
     {
 	long _idx = PyLong_AsLong(idx);
 	return RangeItem((RangeObject *)(self), _idx);
-    } else if (PySlice_Check(idx))
+    }
+    else if (PySlice_Check(idx))
     {
 	Py_ssize_t start, stop, step, slicelen;