Bug 2225532

Description of problem:

rust was updated to 1.71.0 on centos stream 9 causing FTBFS issues with 389-ds-base-2.3.4-3.el9

Issue #1:

error: using `.borrow()` on a double reference, which returns `&concread::cowcell::CowCellReadTxn<CacheStats>` instead of borrowing the inner type
  --> librslapd/src/cache.rs:60:28
   |
60 |     let stats = stat_rguard.borrow();
   |                            ^^^^^^^^^
   |
note: the lint level is defined here
  --> librslapd/src/lib.rs:1:9
   |
1  | #![deny(warnings)]
   |         ^^^^^^^^
   = note: `#[deny(suspicious_double_ref_op)]` implied by `#[deny(warnings)]`
error: could not compile `librslapd` (lib) due to previous error

This is also reported as bug#2225471

Issue #2:

error: variable does not need to be mutable
   --> slapi_r_plugin/src/value.rs:185:13
    |
185 |         let mut v = unsafe { slapi_value_new() };
    |             ----^
    |             |
    |             help: remove this `mut`
    |
note: the lint level is defined here
   --> slapi_r_plugin/src/lib.rs:1:9
    |
1   | #![deny(warnings)]
    |         ^^^^^^^^
    = note: `#[deny(unused_mut)]` implied by `#[deny(warnings)]`
error: could not compile `slapi_r_plugin` (lib) due to previous error

mut is obviously wrong here

Attaching work-around for issue #1 and fix for #2.