tec: Force xdebug version in the Dockerfile

The latest version of xdebug doesn't support PHP 7.4 anymore. We need to
force the version to the latest version which support PHP 7.4.

The other solution would have been to upgrade to a higher PHP version,
but I want it to be the same as the production, which run on Debian.
I’ll update PHP when Debian 12 (Bookworm) will be released.

References:

- https://xdebug.org/docs/compat
- https://chrisshennan.com/blog/fixing-pecl-xdebug-requires-php-version-8-installed-version-7-4
- https://wiki.debian.org/PHP#Available_versions

docker/Dockerfile.php

@@ -13,7 +13,7 @@
         libjpeg62-turbo-dev \
         libpng-dev \
         libwebp-dev \
-    && pecl install xdebug \
+    && pecl install xdebug-3.1.6 \
     && docker-php-ext-configure intl \
     && docker-php-ext-configure gd --with-webp --with-jpeg --with-freetype \
     && docker-php-ext-install -j$(nproc) intl gettext pcntl zip pdo pdo_pgsql gd \