Add Ownable reinitialization check

contracts/attribute/Ownable.sol

@@ -25,6 +25,7 @@ abstract contract Ownable is IOwnable, Initializable {
      * @notice Initializes the contract setting `msg.sender` as the initial owner
      */
     function __Ownable__initialize() internal onlyInitializer {
+        if (owner() != address(0)) revert OwnableAlreadyInitializedError();
         _updateOwner(_sender());
     }
 

contracts/attribute/interfaces/IOwnable.sol

@@ -9,6 +9,7 @@ interface IOwnable is IInitializable {
 
     error OwnableNotOwnerError(address sender);
     error OwnableNotPendingOwnerError(address sender);
+    error OwnableAlreadyInitializedError();
 
     function owner() external view returns (address);
     function pendingOwner() external view returns (address);

contracts/mocks/MockOwnable.sol

@@ -10,6 +10,10 @@ contract MockOwnable is Ownable {
         super.__Ownable__initialize();
     }
 
+    function __initializeV(uint256 version) external initializer(version) {
+        super.__Ownable__initialize();
+    }
+
     function _beforeAcceptOwner() internal override {
         beforeCalled = true;
     }

test/unit/attribute/Ownable.test.ts

@@ -25,6 +25,17 @@ describe('Ownable', () => {
 
       expect(await ownable.owner()).to.equal(owner.address)
     })
+
+    it('reverts if owner already set (reinitializing)', async () => {
+      expect(await ownable.owner()).to.equal(ethers.constants.AddressZero)
+
+      // mock the owner being set in a previous implementation version
+      await ownable.connect(owner).__initializeV(1)
+
+      await expect(ownable.connect(owner).__initializeV(2)).to.revertedWith('OwnableAlreadyInitializedError')
+
+      expect(await ownable.owner()).to.equal(owner.address)
+    })
   })
 
   describe('#setPendingOwner', async () => {