`if` conditional marked as error if the YAML string is double quoted

**Describe the bug**
I have an `if` in my workflow that looks like this:
```yaml
if: "!startsWith(matrix.os, 'ubuntu-')"
```

The conditional is quoted because `!` has meaning in YAML to change the type, so we can't start a string with that character without a way to tell the YAML parser it's a string. **This works fine in the workflow.**

However, it's marked as an error by this extension:

> Unexpected symbol: '"'. Located at position 1 within expression: "!startsWith(matrix.os, 'ubuntu-')"

**Workarounds that work**
* Single quotes (**NOTE** double quotes can't be used inside expression apparently)
* YAML multi-line strings
* Unnecessary templating

```yaml
---
# Note double single quotes internally
if: '!startsWith(matrix.os, ''ubuntu-'')'

---
if: >-
!startsWith(matrix.os, 'ubuntu-')

---
if: ${{ !startsWith(matrix.os, 'ubuntu-') }}
```

**Workarounds that don't work**
* explicit `str` typing

```yaml
---
if: !!str !startsWith(matrix.os, 'ubuntu-')
```

**To Reproduce**
Use a double quoted condition.

**Expected behavior**
No error.

**Screenshots**

**Extension Version**
`v0.25.3`

Reproduce the problem in the GitHub Actions extension using the double-quoted condition shown in the issue, then compare it with the listed working and failing YAML forms. Trace the expression validation path responsible for the unexpected quote error; done means the quoted condition is accepted without an error while existing valid forms continue to work.

Escrita pelo modelo de indexação a partir do texto da issue.