fix (InnerProductSpace.Basic): make toSesqForm noncomputable (#6512)

Explicitly marks `ContinuousLinearMap.toSesqForm` as `noncomputable` to prevent runaway build process which does produces nothing.

Mathlib/Analysis/InnerProductSpace/Basic.lean

@@ -1817,11 +1817,12 @@ namespace ContinuousLinearMap
 
 variable {E' : Type*} [NormedAddCommGroup E'] [InnerProductSpace 𝕜 E']
 
+-- Note: odd and expensive build behavior is explicitly turned off using `noncomputable`
 set_option maxHeartbeats 500000 in
 set_option synthInstance.maxHeartbeats 100000 in
 /-- Given `f : E →L[𝕜] E'`, construct the continuous sesquilinear form `fun x y ↦ ⟪x, A y⟫`, given
 as a continuous linear map. -/
-def toSesqForm : (E →L[𝕜] E') →L[𝕜] E' →L⋆[𝕜] E →L[𝕜] 𝕜 :=
+noncomputable def toSesqForm : (E →L[𝕜] E') →L[𝕜] E' →L⋆[𝕜] E →L[𝕜] 𝕜 :=
   (ContinuousLinearMap.flipₗᵢ' E E' 𝕜 (starRingEnd 𝕜) (RingHom.id 𝕜)).toContinuousLinearEquiv ∘L
     ContinuousLinearMap.compSL E E' (E' →L⋆[𝕜] 𝕜) (RingHom.id 𝕜) (RingHom.id 𝕜) (innerSLFlip 𝕜)
 #align continuous_linear_map.to_sesq_form ContinuousLinearMap.toSesqForm