Update matplotlib requirement from <3.8.0,>3.1 to >3.1,<3.9.0 in /requirements (#18757)

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Carlos Mocholí <[email protected]>

Author: dependabot[bot]

requirements/pytorch/extra.txt

@@ -2,7 +2,7 @@
 #  in case you want to preserve/enforce restrictions on the latest compatible version, add "strict" as an in-line comment
 
 # extended list of package dependencies to reach full functionality
-matplotlib>3.1, <3.8.0
+matplotlib>3.1, <3.9.0
 omegaconf >=2.0.5, <2.4.0
 hydra-core >=1.0.5, <1.4.0
 jsonargparse[signatures] >=4.18.0, <4.26.0

src/lightning/pytorch/tuner/lr_finder.py

@@ -154,7 +154,7 @@ def plot(self, suggest: bool = False, show: bool = False, ax: Optional["Axes"] =
         if ax is None:
             fig, ax = plt.subplots()
         else:
-            fig = ax.figure
+            fig = ax.figure  # type: ignore[assignment]
 
         # Plot loss as a function of the learning rate
         ax.plot(lrs, losses)