use larger disk for build artifacts in CI

I was debugging an issue where my CI jobs were running out of disk space:
```
=== df -h ===
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        72G   71G  1.2G  99% /
tmpfs           7.9G   84K  7.9G   1% /dev/shm
tmpfs           3.2G  1.1M  3.2G   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
/dev/sdb16      881M   62M  758M   8% /boot
/dev/sdb15      105M  6.2M   99M   6% /boot/efi
/dev/sda1        74G  4.1G   66G   6% /mnt
tmpfs           1.6G   12K  1.6G   1% /run/user/1001
=== Top directories in workspace ===
sort: write failed: 'standard output': Broken pipe
16G	./target/debug
16G	./target
16G	.
15G	./target/debug/deps
1.5G	./target/debug/examples
348M	./target/debug/build
19M	./target/debug/.fingerprint
```

See how `/` is 99% full. It turns out that `Swatinem/rust-cache@v2` was caching some outdated artifacts, causing `./target/debug` to be 3-4GB too large.
I was able to fix the issue by reseting the cache, however,  the disk usage is still quite high.
```
=== df -h ===
Filesystem      Size  Used Avail Use% Mounted on
/dev/root        72G   66G  5.8G  93% /
tmpfs           7.9G   84K  7.9G   1% /dev/shm
tmpfs           3.2G  1.2M  3.2G   1% /run
tmpfs           5.0M     0  5.0M   0% /run/lock
/dev/sda16      881M   62M  758M   8% /boot
/dev/sda15      105M  6.2M   99M   6% /boot/efi
/dev/sdb1        74G  4.1G   66G   6% /mnt
tmpfs           1.6G   12K  1.6G   1% /run/user/1001
=== Top directories in workspace ===
12G	./target/debug
12G	./target
12G	.
9.2G	./target/debug/deps
2.2G	./target/debug/examples
200M	./target/debug/build
```

I did some research while debugging this and uncovered that it is common to use `mnt` for cargo artifacts. This change makes cargo use `mnt` for the `target` directory.

Author: jayshrivastava

.github/actions/setup/action.yml

@@ -17,6 +17,13 @@ runs:
         echo $HOME
         echo ${{ runner.os }}
 
+    - shell: bash
+      run: |
+        # Create target directory if CARGO_TARGET_DIR is set
+        if [ -n "$CARGO_TARGET_DIR" ]; then
+          sudo mkdir -p "$CARGO_TARGET_DIR" && sudo chown -R $USER:$USER "$CARGO_TARGET_DIR"
+        fi
+
     - uses: dtolnay/rust-toolchain@stable
       with:
         toolchain: stable

.github/workflows/ci.yml

@@ -9,6 +9,7 @@ on:
 env:
   CARGO_TERM_COLOR: always
   RUST_BACKTRACE: 1
+  CARGO_TARGET_DIR: /mnt/target
 
 concurrency:
   group: ${{ github.ref }}
@@ -32,6 +33,15 @@ jobs:
           lfs: true
       - uses: ./.github/actions/setup
       - run: cargo test --features integration
+      - name: Show disk usage
+        if: always()
+        run: |
+          echo "=== df -h ==="
+          df -h
+          echo "=== top directories in workspace  ==="
+          du -h . 2>/dev/null | sort -hr | head -n 10 || true
+          echo "=== cargo target directory ==="
+          du -sh /mnt/target 2>/dev/null || true
 
   tpch-test:
     runs-on: ubuntu-latest