ci: re-pin reusable workflow ref to resq-software/.github main

Updates @sha from the feat-branch tip to the merge commit of
resq-software/.github#12 (f4b51a620aa1bf89c0bce4f434b36f92ff7d517d). Functionally equivalent — same
content — but pins to a ref that now exists on main rather than a
closed PR branch.

Author: WomB0ComB0

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ concurrency:
 
 jobs:
   rust:
-    uses: resq-software/.github/.github/workflows/rust-ci.yml@5a723728feccfc5521dc4e5cb06237892d393553
+    uses: resq-software/.github/.github/workflows/rust-ci.yml@f4b51a620aa1bf89c0bce4f434b36f92ff7d517d
     with:
       toolchain: stable
       run-fmt: true