Bump pallet-staking-reward-fn (#10905)

Bump pallet-staking-reward-fn to patch. This forces it to use local path
and the local sp-arithmetic instead of registry while running
`parity-publish`.
This aims to fix the failure in `Check publish build` job (e.g.
https://github.com/paritytech/polkadot-sdk/actions/runs/21359458014/job/61474963706?pr=10903#step:12:546)
which started to appear since #10682 got merged.

When parity-publish is used with --registry:
- If the version exists on crates.io → remove path, use registry
- If the version doesn't exist → keep path, use local
The issue is that --registry creates a hybrid state where some deps use
registry and some use local paths, causing version conflicts in case e.g
of missing trait impl in on the two.

Extended explanation, courtesy of @iulianbarbu : 
In the parity-publish CI job example we have:
- polkadot-runtime-common (crate A), depends on crate B indirectly &
crate C
- sp-arithmetic (crate B), was bumped locally (due to #10682), but not
published on the registry yet
- pallet-staking-reward-fn (crate C). depends on crate B.

polkadot-runtime-common fails to compile due to a dependency graph using
two versions of same type of crate B. What is an issue though is that
pallet-staking-reward-fn uses the previous crate B version (from the
registry), which misses a certain trait impl that is required by
polkadot-runtime-common. If polkadot-runtime-common usage of
pallet-staking-reward-fn expects the new trait impl, it means that it is
not enough to just bump pallet-staking-reward-fn, but also
polkadot-runtime-common, in this PR (to update it to depend on the new
version of pallet-staking-reward-fn). Everything compiles fine rn
because polkadot-runtime-common is already bumped in a previous PR (e.g
#10582 and maybe others), which did not make its way to a stable release
yet.

Author: sigurpol

prdoc/pr_10905.prdoc

@@ -0,0 +1,11 @@
+title: 'Bump pallet-staking-reward-fn'
+doc:
+- audience: Runtime Dev
+  description: |-
+    sp-arithmetic was bumped in a previous PR but not published yet on crates.io.
+    Both polkadot-runtime-common (already bumped and not released in a previous PR) and pallet-staking-reward-fn depend on it.
+    Bump pallet-staking-reward-fn so that parity-publish CI job can correctly resolve sp-arithmetic.
+    Without this fix, we would end up with a dependency graph with two versions of sp-arithmetic with one of the two missing a trait impl needed by polkadot-runtime-common.
+crates:
+- name: pallet-staking-reward-fn
+  bump: patch