Suppress exception chaining in FontProperties.

For `FontProperties(stretch=12345)`; before:
```
Traceback (most recent call last):
  File ".../matplotlib/font_manager.py", line 888, in set_stretch
    raise ValueError()
ValueError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File ".../matplotlib/font_manager.py", line 695, in __init__
    self.set_stretch(stretch)
  File ".../matplotlib/font_manager.py", line 891, in set_stretch
    raise ValueError("stretch is invalid") from err
ValueError: stretch is invalid
```
after
```
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File ".../matplotlib/font_manager.py", line 695, in __init__
    self.set_stretch(stretch)
  File ".../matplotlib/font_manager.py", line 900, in set_stretch
    raise ValueError(f"{stretch=} is invalid")
ValueError: stretch=12345 is invalid
```

Author: anntzer

lib/matplotlib/font_manager.py

@@ -860,14 +860,18 @@ def set_weight(self, weight):
         """
         if weight is None:
             weight = rcParams['font.weight']
+        if weight in weight_dict:
+            self._weight = weight
+            return
         try:
             weight = int(weight)
-            if weight < 0 or weight > 1000:
-                raise ValueError()
         except ValueError:
-            if weight not in weight_dict:
-                raise ValueError("weight is invalid")
-        self._weight = weight
+            pass
+        else:
+            if 0 <= weight <= 1000:
+                self._weight = weight
+                return
+        raise ValueError(f"{weight=} is invalid")
 
     def set_stretch(self, stretch):
         """
@@ -882,14 +886,18 @@ def set_stretch(self, stretch):
         """
         if stretch is None:
             stretch = rcParams['font.stretch']
+        if stretch in stretch_dict:
+            self._stretch = stretch
+            return
         try:
             stretch = int(stretch)
-            if stretch < 0 or stretch > 1000:
-                raise ValueError()
         except ValueError as err:
-            if stretch not in stretch_dict:
-                raise ValueError("stretch is invalid") from err
-        self._stretch = stretch
+            pass
+        else:
+            if 0 <= stretch <= 1000:
+                self._stretch = stretch
+                return
+        raise ValueError(f"{stretch=} is invalid")
 
     def set_size(self, size):
         """