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

@@ -26,7 +26,7 @@ concurrency:
 
 jobs:
   gates:
-    uses: resq-software/.github/.github/workflows/required.yml@6410acba18c9fc79949643abd48f0a2d43994c62
+    uses: resq-software/.github/.github/workflows/required.yml@f4b51a620aa1bf89c0bce4f434b36f92ff7d517d
     with:
       lang: cpp
       cpp-os-list: '["ubuntu-latest","macos-latest","windows-latest"]'