Constants are considered pure.

test/libsolidity/syntaxTests/inheritance/override/public_constant_var_overrides_pure.sol

@@ -0,0 +1,7 @@
+abstract contract C {
+    function foo() external pure virtual returns (uint);
+}
+contract X is C {
+	uint public constant override foo = 7;
+}
+// ----

test/libsolidity/syntaxTests/inheritance/override/public_immutable_var_overrides_pure.sol

@@ -0,0 +1,8 @@
+abstract contract C {
+    function foo() external pure virtual returns (uint);
+}
+contract X is C {
+	uint public immutable override foo = 7;
+}
+// ----
+// TypeError 6959: (100-124): Overriding public state variable changes state mutability from "pure" to "view".