Fix Hypatia setup-beam ubuntu24 support (Issue #516)

Issue #516: Hypatia: setup-beam pin cannot map ImageOS=ubuntu24

Update erlef/setup-beam from 54075bcc5e249e4758d363f27d099f55d843f124
to 8736e9244717f9207464c14c6051b71d22253f60 (latest main) in:
- .github/workflows/hypatia-scan-reusable.yml
- .github/workflows/elixir-ci-reusable.yml

The old pin predates ubuntu24 support. ubuntu-latest now resolves to Ubuntu 24.04,
which sets ImageOS=ubuntu24, causing setup-beam to fail with:
  'Tried to map a target OS from env. variable ImageOS (got ubuntu24), but failed.'

The new commit includes ubuntu24 mapping, allowing Hypatia scanner to run on
all callers using ubuntu-latest runners.

Part of estate-wide CI/CD deduplication.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

Author: hyperpolymath

.github/workflows/elixir-ci-reusable.yml

@@ -158,7 +158,7 @@ jobs:
           ref: ${{ github.ref }}
 
       - name: Set up BEAM (OTP + Elixir)
-        uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
+        uses: erlef/setup-beam@8736e9244717f9207464c14c6051b71d22253f60 # v1.24.1
         with:
           otp-version: ${{ inputs.otp-version }}
           elixir-version: ${{ inputs.elixir-version }}

.github/workflows/hypatia-scan-reusable.yml

@@ -22,7 +22,7 @@ jobs:
           fetch-depth: 0
 
       - name: Setup Elixir for Hypatia scanner
-        uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
+        uses: erlef/setup-beam@8736e9244717f9207464c14c6051b71d22253f60 # v1.24.1
         with:
           elixir-version: '1.19.4'
           otp-version: '28.3'