chore(server): Bump PHP in server image

[nickvergessen]

@tobiasKaminsky The image seems to be from you? It can no longer build as the full server repo with history is too big to be cloned in the builders

https://github.com/nextcloud/docker-ci/actions/runs/18195103803/job/51799192838?pr=829

System.IO.IOException: Disk quota exceeded : '/home/runner/actions-runner/_diag/Worker_20251002-135305-utc.log'
   at System.IO.RandomAccess.WriteAtOffset(SafeFileHandle handle, ReadOnlySpan`1 buffer, Int64 fileOffset)
   at System.IO.StreamWriter.Flush(Boolean flushStream, Boolean flushEncoder)
   at System.Diagnostics.TextWriterTraceListener.Flush()
   at GitHub.Runner.Common.HostTraceListener.WriteHeader(String source, TraceEventType eventType, Int32 id)
   at System.Diagnostics.TraceSource.TraceEvent(TraceEventType eventType, Int32 id, String message)
   at GitHub.Runner.Worker.Worker.RunAsync(String pipeIn, String pipeOut)
   at GitHub.Runner.Worker.Program.MainAsync(IHostContext context, String[] args)