[CssSelector] Fix URL to SimonSapin/cssselect repo
minor #11779 [CssSelector] Fix URL to SimonSapin/cssselect repo in README (jwpage)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #11779).

Discussion
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[CssSelector] Fix URL to SimonSapin/cssselect repo in README

This fixes a broken link in the CssSelector README spotted by @philsturgeon in https://github.com/symfony/CssSelector/pull/2.

| Q             | A
| ------------- | ---
| Fixed tickets | none
| License       | MIT

Commits
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b9a237c [CssSelector] Fix URL to SimonSapin/cssselect repo