CI: Disable cleanup of docker/setup-buildx-action

It started to fail with the following error (for no obvious reason):
```
/nvme/actions-runner/_work/_actions/docker/setup-buildx-action/v3/webpack:/docker-setup-buildx/node_modules/@actions/cache/lib/cache.js:175
            throw new Error(`Path Validation Error: Path(s) specified in the action for caching do(es) not exist, hence no cache is being saved.`);
^
Error: Path Validation Error: Path(s) specified in the action for caching do(es) not exist, hence no cache is being saved.
    at Object.rejected (/nvme/actions-runner/_work/_actions/docker/setup-buildx-action/v3/webpack:/docker-setup-buildx/node_modules/@actions/cache/lib/cache.js:175:1)
    at Generator.next (<anonymous>)
    at fulfilled (/nvme/actions-runner/_work/_actions/docker/setup-buildx-action/v3/webpack:/docker-setup-buildx/node_modules/@actions/cache/lib/cache.js:29:1)
```

.github/workflows/build_and_test.yml

@@ -736,6 +736,11 @@ jobs:
           mkdir -p .docker-custom
           echo DOCKER_CONFIG=$(pwd)/.docker-custom >> $GITHUB_ENV
       - uses: docker/setup-buildx-action@v3
+        with:
+          # Disable cleanup to work-around failure at post-run stage:
+          # "Path Validation Error: Path(s) specified in the action for caching do(es) not exist, hence no cache is being saved."
+          # See also https://github.com/neondatabase/neon/pull/7445
+          cleanup: false
 
       - uses: docker/login-action@v3
         with:
@@ -799,6 +804,10 @@ jobs:
           config-inline: |
             [worker.oci]
               max-parallelism = 1
+          # Disable cleanup to work-around failure at post-run stage:
+          # "Path Validation Error: Path(s) specified in the action for caching do(es) not exist, hence no cache is being saved."
+          # See also https://github.com/neondatabase/neon/pull/7445
+          cleanup: false
 
       - uses: docker/login-action@v3
         with: