Pin to nonbroken buildx version

Buildx 0.13.0 appears to break caching:
moby/buildkit#4765

We've also seen this:
https://github.com/PrefectHQ/prefect/actions/runs/8299698555/job/22718642247?pr=12323

Pin to 0.12.5 to see if that prevents the issue.

.github/workflows/benchmarks.yaml

@@ -40,6 +40,8 @@ jobs:
       - name: Set up Docker Buildx
         if: ${{ matrix.build-docker-images }}
         uses: docker/setup-buildx-action@v3
+        with:
+          version: v0.12.5
 
       - name: Set up Python 3.10
         uses: actions/setup-python@v5

.github/workflows/docker-images.yaml

@@ -34,6 +34,8 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
+        with:
+          version: v0.12.5
 
       - name: Login to DockerHub
         uses: docker/login-action@v3

.github/workflows/python-tests.yaml

@@ -75,6 +75,8 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
+        with:
+          version: v0.12.5
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5
@@ -227,6 +229,8 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
+        with:
+          version: v0.12.5
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5
@@ -386,6 +390,8 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
+        with:
+          version: v0.12.5
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5
@@ -581,6 +587,8 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
+        with:
+          version: v0.12.5
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5