Fix Trivy diskspace issue by cleaning docker build cache (#35059)

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**Related issue:** Resolves #35057

Ran successfully. Now fails with CVEs and not disk space issues:
https://github.com/fleetdm/fleet/actions/runs/18977076930/job/54199504988

.github/workflows/build-fleetdm-bomutils-check-vulnerabilities.yml

@@ -41,6 +41,11 @@ jobs:
       - name: Build fleetdm/bomutils
         run: make bomutils-docker
 
+      - name: Clean up Docker build cache
+        run: |
+          docker system prune -af
+          df -h
+
       - name: List VEX files
         id: generate_vex_files
         run: |

.github/workflows/build-fleetdm-fleetctl-check-vulnerabilities.yml

@@ -41,6 +41,11 @@ jobs:
       - name: Build fleetdm/fleetctl
         run: make fleetctl-docker
 
+      - name: Clean up Docker build cache
+        run: |
+          docker system prune -af
+          df -h
+
       - name: List VEX files
         id: generate_vex_files
         run: |

.github/workflows/build-fleetdm-wix-check-vulnerabilities.yml

@@ -41,6 +41,11 @@ jobs:
       - name: Build fleetdm/wix
         run: make wix-docker
 
+      - name: Clean up Docker build cache
+        run: |
+          docker system prune -af
+          df -h
+
       - name: List VEX files
         id: generate_vex_files
         run: |