Bump php from 7-fpm to 8-fpm in /example/php/jaeger

Bumps php from 7-fpm to 8-fpm.

---
updated-dependencies:
- dependency-name: php
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

example/php/jaeger/Dockerfile

@@ -1,4 +1,4 @@
-FROM php:7-fpm
+FROM php:8-fpm
 
 WORKDIR /var/www/app
 ADD . /var/www/app