Added a spread bound check in the setSpread function (#9252)

### Description

_A few sentences describing the overall effects and goals of the pull request's commits.
What is the current behavior, and what is the updated/expected behavior with this PR?_
I've created a bound check for the spread to make sure that its value never exceeds 1.
### Other changes

_Describe any minor or "drive-by" changes here._

### Tested

_An explanation of how the changes were tested or an explanation as to why they don't need to be._
I've added a condition in the test suite which checks, that the value of spread shouldn't exceed 1.
### Related issues

- Fixes #[issue number here]

### Backwards compatibility

_Brief explanation of why these changes are/are not backwards compatible._

### Documentation

_The set of community facing docs that have been added/modified because of this change_

packages/protocol/contracts/stability/Exchange.sol

@@ -296,6 +296,10 @@ contract Exchange is
     */
   function setSpread(uint256 newSpread) public onlyOwner {
     spread = FixidityLib.wrap(newSpread);
+    require(
+      FixidityLib.lte(spread, FixidityLib.fixed1()),
+      "the value of spread must be less than or equal to 1"
+    );
     emit SpreadSet(newSpread);
   }
 

packages/protocol/test/stability/exchange.ts

@@ -296,7 +296,6 @@ contract('Exchange', (accounts: string[]) => {
 
   describe('#setSpread', () => {
     const newSpread = toFixed(6 / 1000)
-
     it('should set the spread', async () => {
       await exchange.setSpread(newSpread)
 
@@ -305,6 +304,10 @@ contract('Exchange', (accounts: string[]) => {
       assert.isTrue(actualSpread.eq(newSpread))
     })
 
+    it('the spread should always be less than or equal to 1', async () => {
+      await assertRevert(exchange.setSpread(toFixed(1001 / 1000)))
+    })
+
     it('should emit a SpreadSet event', async () => {
       const tx = await exchange.setSpread(newSpread)
       assert(tx.logs.length === 1, 'Did not receive event')