double curly brace can have incorrect syntax highlighting inside format within expression

**Describe the bug**
When a double closing curly brace (`}}` is used as an escape to represent a single closing curly brace (`}`) inside a format function that is within an expression, it gets incorrectly colored as the end of the expression.

**To Reproduce**
Steps to reproduce the behavior:
1. With the workflow file below, open in vscode editor
2. View the syntax highlighting as incorrect. The first double closing curly brace on line 19 should not be yellow.

```
name: Double Curly Brace Workflow

on:
workflow_dispatch:
inputs:
something-to-print:
description: Something to print in powershell.
required: true
type: string

jobs:
double_curly_brace_job:
runs-on:
labels: windows

steps:
- name: Double Curly Brace Step
env:
VAR_WITH_DOUBLE_CURLY_BRACE: "${{ format('{{ {0} }}', inputs.something-to-print) }}"
run: |
echo "${{ env.VAR_WITH_DOUBLE_CURLY_BRACE }}"
```

**Expected behavior**
The last double closing curly brace should be yellow on line 19.

**Screenshots**

**Extension Version**
`v0.26.5`

**Additional context**
I am testing this on Mac OS Sonoma 14.5
`code --version
1.91.1
f1e16e1e6214d7c44d078b1f0607b2388f29d729
x64`

Start by reproducing the workflow in the VS Code editor and inspect how the extension highlights nested GitHub Actions expressions and format strings. Trace the syntax-highlighting entry point for expression parsing, then verify that the escaped double closing brace is not treated as the expression end while the final closing brace remains highlighted.

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