Comma separated rules are unnecessarily expanded (duplicate blocks)

Nobody has claimed this yet.

It appears that comma-separated rules are expanded even if the variable value is the same, creating additional unnecessary rules.

Input:
```css
:root {
--font-family: sans-serif;
}

h1, h2, h3, h4, h5, h6 {
font-family: var(--font-family);
}
```

Expected output:
```css
h1, h2, h3, h4, h5, h6 {
font-family: sans-serif;
}
```

Actual output:
```css
h1 {
font-family: sans-serif;
}

h2 {
font-family: sans-serif;
}

h3 {
font-family: sans-serif;
}

h4 {
font-family: sans-serif;
}

h5 {
font-family: sans-serif;
}

h6 {
font-family: sans-serif;
}
```

Reproduce the issue with the CSS input and expected output shown in the report, then trace the selector expansion performed by the PostCSS plugin. The work is done when identical resolved declarations remain under one comma-separated selector and the output no longer contains duplicate blocks.

Written by the indexing model from the issue text.