chore: bump actions/setup-go from 5 to 6

Bumps [actions/setup-go](https://github.com/actions/setup-go) from 5 to 6.
- [Release notes](https://github.com/actions/setup-go/releases)
- [Commits](https://github.com/actions/setup-go/compare/v5...v6)

---
updated-dependencies:
- dependency-name: actions/setup-go
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/backend-tests.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
           go-version: 1.25
           check-latest: true
@@ -36,7 +36,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v5
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
           go-version: 1.25
           check-latest: true

.github/workflows/build-artifacts.yml

@@ -16,7 +16,7 @@ jobs:
         uses: actions/checkout@v5
         with:
           fetch-depth: 0
-      - uses: actions/setup-go@v5
+      - uses: actions/setup-go@v6
         with:
           go-version: 1.25
           check-latest: true