Add transient storage slot support in StorageSlot.sol (#4980)

Co-authored-by: ernestognw <ernestognw@gmail.com>

test/governance/extensions/GovernorTimelockAccess.test.js

@@ -375,7 +375,7 @@ describe('GovernorTimelockAccess', function () {
             if (delay > 0) {
               await this.helper.waitForEta();
             }
-            expect(await this.helper.execute())
+            await expect(this.helper.execute())
               .to.emit(this.mock, 'ProposalExecuted')
               .withArgs(this.proposal.id)
               .to.emit(this.receiver, 'CalledUnrestricted');