Upgrade XRootD once official patch with getCredentials segfault fix is released

To give a quick summary of the situation:

1. We periodically had segfaults in the XRootD part of the tape servers
2. The stars (mis)alligned
3. The periodic failures turned into extremely frequent failures and test-client started failing 9/10 times
4. I worked together with Guilherme to get a fix. This issue as now been solved.
5. However, his fix is not in an official XRootD release yet, but to unblock the developers we updated main to use this temporary patched version of XRootD from its corresponding testing repo
6. Now what is left to do is wait for an official XRootD release containing this fix so that we can updated

Until we have an official version of XRootD again, we cannot (and should not) be making releases. However, we should see a new XRootD release very soon.

Once this release is there, we should update CTA again to use it.