Use vendoring instead of Go module caching

Replace Go module cache with vendored dependencies shared via artifact.
This is faster and more reliable than caching. Vendor directory is created
once in prepare-dependencies job and shared across all test jobs using
GOFLAGS=-mod=vendor.

Author: zph

.github/workflows/main.yml

@@ -21,29 +21,45 @@ jobs:
       - name: Running ${{ matrix.command }}
         run: ${{ matrix.command }}
 
-  prepare-terraform:
-    name: Prepare Terraform Binary
+  prepare-dependencies:
+    name: Prepare Dependencies
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout Git repo
         uses: actions/checkout@v4
 
+      - name: Set up Go
+        uses: actions/setup-go@v4
+        with:
+          go-version-file: go.mod
+      
       - name: Download Terraform
         run: |
           mkdir -p bin
           curl -sfL https://releases.hashicorp.com/terraform/1.5.6/terraform_1.5.6_linux_amd64.zip > bin/terraform.zip
           cd bin && unzip terraform.zip && rm terraform.zip && chmod +x terraform
       
+      - name: Vendor Go dependencies
+        run: go mod vendor
+      
       - name: Upload Terraform binary
         uses: actions/upload-artifact@v4
         with:
           name: terraform-binary
           path: bin/terraform
           retention-days: 1
+      
+      - name: Upload vendor directory
+        uses: actions/upload-artifact@v4
+        with:
+          name: vendor-dir
+          path: vendor/
+          retention-days: 1
+          compression-level: 6
 
   tests:
     runs-on: ubuntu-22.04
-    needs: [prepare-terraform]
+    needs: [prepare-dependencies]
     strategy:
       fail-fast: false
       matrix:
@@ -72,22 +88,18 @@ jobs:
         with:
           go-version-file: go.mod
 
-      - name: Cache Go modules
-        uses: actions/cache@v4
-        with:
-          path: |
-            ~/.cache/go-build
-            ~/go/pkg/mod
-          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
-          restore-keys: |
-            ${{ runner.os }}-go-
-      
       - name: Download Terraform binary
         uses: actions/download-artifact@v4
         with:
           name: terraform-binary
           path: bin/
 
+      - name: Download vendor directory
+        uses: actions/download-artifact@v4
+        with:
+          name: vendor-dir
+          path: vendor/
+      
       - name: Make Terraform executable
         run: chmod +x bin/terraform
 
@@ -97,6 +109,8 @@ jobs:
           sudo apt-get -f -y install mysql-client
       
       - name: Run tests {{ matrix.target }}
+        env:
+          GOFLAGS: -mod=vendor
         run: make ${{ matrix.target }}
   # DISABLED to figure out GPG signing issue on Github Actions
   #         possibly due to lack of TTY inside docker?