bug(Overlay): FlexibleConnectedPositionStrategy withViewportMargin not working

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

When using overlay with `FlexibleConnectedPositionStrategy` and `withViewportMargin()`, overlay ignores provided margin value and still opens in first preffered position, when it should move to second one. Overlay cant be pushed and has no flexible dimmensions set.

### Reproduction

https://stackblitz.com/edit/viewport-margin-bug?file=src%2Fapp%2Fapp.component.ts
(Red line shows 100px margin edge)

Steps to reproduce:
1. Create overlay with popup 100px x 100px
2. Locate its origin point 150px from top edge of viewport.
3. Add two positions to FlexibleConnectedPositionStrategy:
```
{
originX: 'end',
originY: 'top',
overlayX: 'start',
overlayY: 'bottom',
},
{
originX: 'end',
originY: 'bottom',
overlayX: 'start',
overlayY: 'top',
},
```
4. Use `withViewportMargin(100)`.
5. Use `withFlexibleDimensions(false)`
6. Use `withPush(false)`

### Expected Behavior

Since `withViewPortMargin(100)` was set, and overlay cannot be pushed or shrinked, then it should fallback to second preffered position in which popup opens downwards.
```
{
originX: 'end',
originY: 'bottom',
overlayX: 'start',
overlayY: 'top',
},
```

### Actual Behavior

Overlay still opens according to first position which is upward, ignoring viewport margin

### Environment

- Angular: 13.1.3
- CDK/Material: 13.1.3
- Browser(s): Chrome 97
- Operating System (e.g. Windows, macOS, Ubuntu): macOS

Start with the linked StackBlitz reproduction and inspect FlexibleConnectedPositionStrategy, focusing on how withViewportMargin interacts with disabled flexible dimensions and push behavior. Done means the overlay falls back to the second position when the first violates the 100px viewport margin, with coverage for the reported configuration.

Written by the indexing model from the issue text.