chore: fix typo intIsManifoldModelSpace (#24297)

Rename `intIsManifoldModelSpace` to `instIsManifoldModelSpace`.

Author: peabrainiac

Mathlib/Geometry/Manifold/IsManifold/Basic.lean

@@ -690,11 +690,14 @@ theorem isManifold_of_contDiffOn {𝕜 : Type*} [NontriviallyNormedField 𝕜]
 alias smoothManifoldWithCorners_of_contDiffOn := isManifold_of_contDiffOn
 
 /-- For any model with corners, the model space is a `C^n` manifold -/
-instance intIsManifoldModelSpace {𝕜 : Type*} [NontriviallyNormedField 𝕜] {E : Type*}
+instance instIsManifoldModelSpace {𝕜 : Type*} [NontriviallyNormedField 𝕜] {E : Type*}
     [NormedAddCommGroup E] [NormedSpace 𝕜 E] {H : Type*} [TopologicalSpace H]
     {I : ModelWithCorners 𝕜 E H} {n : WithTop ℕ∞} : IsManifold I n H :=
   { hasGroupoid_model_space _ _ with }
 
+@[deprecated (since := "2025-04-22")]
+alias intIsManifoldModelSpace := instIsManifoldModelSpace
+
 end IsManifold
 
 namespace IsManifold