fix: pin musl 1.2.5 for DNS fixes (#6189)

## Summary
musl 1.2.5 includes [several fixes to DNS over
TCP](https://www.openwall.com/lists/musl/2024/03/01/2), which appears to
be the root cause of #6116.

This approach is a bit janky, but according to codex:
> On the Ubuntu 24.04 runners we use, apt-cache policy musl-tools shows
only the distro build (1.2.4-2ubuntu2)"

We should build with this version and confirm.

## Testing
- [ ] TODO: test and see if this fixes Azure issues

.github/workflows/rust-ci.yml

@@ -217,14 +217,10 @@ jobs:
           key: apt-${{ matrix.runner }}-${{ matrix.target }}-v1
 
       - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
-        name: Install musl build tools
-        env:
-          DEBIAN_FRONTEND: noninteractive
-        shell: bash
-        run: |
-          set -euo pipefail
-          sudo apt-get -y update -o Acquire::Retries=3
-          sudo apt-get -y install --no-install-recommends musl-tools pkg-config
+        name: Setup musl 1.2.5 toolchain
+        uses: ./.github/actions/setup-musl-1_2_5
+        with:
+          target: ${{ matrix.target }}
 
       - name: Install cargo-chef
         if: ${{ matrix.profile == 'release' }}

.github/workflows/rust-release.yml

@@ -92,10 +92,10 @@ jobs:
           key: cargo-${{ matrix.runner }}-${{ matrix.target }}-release-${{ hashFiles('**/Cargo.lock') }}
 
       - if: ${{ matrix.target == 'x86_64-unknown-linux-musl' || matrix.target == 'aarch64-unknown-linux-musl'}}
-        name: Install musl build tools
-        run: |
-          sudo apt-get update
-          sudo apt-get install -y musl-tools pkg-config
+        name: Setup musl 1.2.5 toolchain
+        uses: ./.github/actions/setup-musl-1_2_5
+        with:
+          target: ${{ matrix.target }}
 
       - name: Cargo build
         run: cargo build --target ${{ matrix.target }} --release --bin codex --bin codex-responses-api-proxy