fix: enable Go module caching in coverage steps action (#1996)

Add cache: true and cache-dependency-path to setup-go action to prevent
network issues when downloading Go modules during coverage testing.

This fixes Forbidden errors from storage.googleapis.com proxy by
utilizing GitHub Actions' built-in Go module caching mechanism.

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Nikolai Emil Damm <[email protected]>

Author: 3 people

.github/actions/daily-test-improver/coverage-steps/action.yml

@@ -4,11 +4,13 @@ description: Builds the project, runs tests, and generates coverage reports
 runs:
   using: composite
   steps:
-    # Step 1: Setup Go environment
+    # Step 1: Setup Go environment with module caching
     - name: ⚙️ Setup Go
       uses: actions/setup-go@7a3fe6cf4cb3a834922a1244abfce67bcef6a0c5 # v6.2.0
       with:
         go-version-file: go.mod
+        cache: true
+        cache-dependency-path: go.sum
 
     # Step 2: Verify Go installation
     - name: ✅ Verify Go setup