;ci: linux: free and show disk space

To help with disk space failures in the last couple of PR builds.
Seems to be https://github.com/actions/virtual-environments/issues/709.

.github/workflows/linux.yml

@@ -128,6 +128,26 @@ jobs:
           ${{ runner.os }}-hledger-web-stack-work-${{ matrix.plan.key }}
           ${{ runner.os }}-hledger-web-stack-work
 
+    - name: Free disk space
+      run: |
+        df -h /
+        sudo swapoff -a
+        df -h /
+        ls -lh /swapfile
+        sudo rm -f /swapfile
+        df -h /
+        sudo apt clean
+        df -h /
+        docker image ls -aq
+        docker rmi $(docker image ls -aq)
+        df -h /
+        find ~/work/_temp -name "cache.tgz" -exec rm -f {} \;
+        df -h /
+        sudo rm -rf "/usr/local/share/boost"
+        df -h /
+        sudo rm -rf "$AGENT_TOOLSDIRECTORY"
+        df -h /
+
     # actions
 
     - name: Install stack
@@ -140,7 +160,10 @@ jobs:
 
     - name: Install GHC
       run: |
+        df -h
         stack $ARGS setup --install-ghc
+        df -h
+
       env:
         ARGS: ${{ matrix.plan.args }}