fix deprecation of I (#25666)

* fix deprecation of I

Author: fredrikekre

base/deprecated.jl

@@ -1368,7 +1368,6 @@ end
 @deprecate_moved copy_transpose! "LinearAlgebra" false true
 @deprecate_moved issuccess       "LinearAlgebra" false true
 @deprecate_moved transpose_type  "LinearAlgebra" false true
-@deprecate_moved I               "LinearAlgebra" false true
 @deprecate_moved A_mul_B!        "LinearAlgebra" false true
 @deprecate_moved A_mul_Bt!       "LinearAlgebra" false true
 @deprecate_moved At_mul_B!       "LinearAlgebra" false true

base/sysimg.jl

@@ -553,6 +553,8 @@ Base.require(Base, :Unicode)
 
     # PR #25571
     @deprecate_binding LinAlg root_module(Base, :LinearAlgebra) true ", run `using LinearAlgebra` instead"
+    @deprecate_binding(I, root_module(Base, :LinearAlgebra).I, true,
+        ", run `using LinearAlgebra` to load linear algebra functionality.")
 end
 
 empty!(DEPOT_PATH)