Description of problem:
Current SELinux policies doesn't allow new systemd credentials feature. E.g. running a command like this:

```
sudo systemd-run -P --wait -p LoadCredential=abc:/etc/hosts systemd-creds cat abc
```

Results in:

run-u11509.service: Failed to set up credentials: Protocol error
run-u11509.service: Failed at step CREDENTIALS spawning /bin/systemd-creds: Protocol error
run-u11509.service: Main process exited, code=exited, status=243/CREDENTIALS
run-u11509.service: Failed with result 'exit-code'.

And audit.log:
type=PROCTITLE msg=audit(12/06/2022 14:32:29.129:410) : proctitle=(sd-mkdcreds)
type=SYSCALL msg=audit(12/06/2022 14:32:29.129:410) : arch=x86_64 syscall=openat success=no exit=EACCES(Permission denied) a0=0x3 a1=0x55a11385ef90 a2=O_RDWR|O_CREAT|O_EXCL|O_NOCTTY|O_NOFOLLOW|O_CLOEXEC a3=0x180 items=0 ppid=3368570 pid=3368571 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=(sd-mkdcreds) exe=/usr/lib/systemd/systemd subj=system_u:system_r:init_t:s0 key=(null)
type=AVC msg=audit(12/06/2022 14:32:29.129:410) : avc:  denied  { read write open } for  pid=3368571 comm=(sd-mkdcreds) path=/dev/shm/.#cred8d2badcefa7a5141 dev="ramfs" ino=365308391 scontext=system_u:system_r:init_t:s0 tcontext=system_u:object_r:ramfs_t:s0 tclass=file permissive=0

This seems to be because selinux forbids systemd process to create ramfs files. Adding such permission with semodule containing the following permissions fixes the problem:

allow init_t ramfs_t:file { create open read rename setattr write };


Version-Release number of selected component (if applicable):
CentOS Stream 9
selinux-policy-targeted: 38.1.3


How reproducible:
Everytime

Steps to Reproduce:
1. Make sure selinux is enabled
2. sudo systemd-run -P --wait -p LoadCredential=abc:/etc/hosts systemd-creds cat abc

Actual results:
Main processes terminated with: code=exited/status=243

Expected results:
Contents of /etc/hosts file

Additional info:

Compiling and installing semodule with the following permissions fixes the issue:
allow init_t ramfs_t:file { create open read rename setattr write };