Create symlink on GitHub Actions runner in /srv/www that points to th…

…e repository checkout

There are some hardcoded paths in the config that are hard to change and are needed for rendering the blog post template:
- SRI extension path to CSS, JS etc.
- SVG icons paths

These could be set/overwritten in the test with

```php
$this->sriConfig->setLocalPrefix((object)['path' => __DIR__ . '/../../../public/www.michalspacek.cz']);
PrivateProperty::setValue($this->svgIconNodeFactory, 'iconsDir', __DIR__ . '/../../../node_modules/humbleicons/icons');
```
But then you get "Cannot modify readonly property Spaze\SvgIcons\Nodes\IconNodeFactory::$iconsDir"

Creating a custom template where neither SRI nor SVG icons are needed would be possible but then things like "Component with name 'articleHeaderIcons' does not exist" from #169 would not be tested.

.github/workflows/php.yml

@@ -197,6 +197,10 @@ jobs:
       with:
         coverage: pcov
         php-version: ${{ matrix.php-version }}
+    - name: Create symlink in /srv/www
+      run: |
+        sudo mkdir --parents /srv/www
+        sudo ln --symbolic $GITHUB_WORKSPACE /srv/www
     - run: make --directory=site tester
     - name: Failed test output, if any
       if: failure()