Add artifacts test fixture (#30300)

Closes https://github.com/go-gitea/gitea/issues/30296

- Adds a DB fixture for actions artifacts
- Adds artifacts test files
- Clears artifacts test files between each run
- Note: I initially initialized the artifacts only for artifacts tests,
but because the files are small it only takes ~8ms, so I changed it to
always run in test setup for simplicity
- Fix some otherwise flaky tests by making them not depend on previous
tests

models/fixtures/action_artifact.yml

@@ -0,0 +1,71 @@
+-
+  id: 1
+  run_id: 791
+  runner_id: 1
+  repo_id: 4
+  owner_id: 1
+  commit_sha: c2d72f548424103f01ee1dc02889c1e2bff816b0
+  storage_path: "26/1/1712166500347189545.chunk"
+  file_size: 1024
+  file_compressed_size: 1024
+  content_encoding: ""
+  artifact_path: "abc.txt"
+  artifact_name: "artifact-download"
+  status: 1
+  created_unix: 1712338649
+  updated_unix: 1712338649
+  expired_unix: 1720114649
+
+-
+  id: 19
+  run_id: 791
+  runner_id: 1
+  repo_id: 4
+  owner_id: 1
+  commit_sha: c2d72f548424103f01ee1dc02889c1e2bff816b0
+  storage_path: "26/19/1712348022422036662.chunk"
+  file_size: 1024
+  file_compressed_size: 1024
+  content_encoding: ""
+  artifact_path: "abc.txt"
+  artifact_name: "multi-file-download"
+  status: 2
+  created_unix: 1712348022
+  updated_unix: 1712348022
+  expired_unix: 1720124022
+
+-
+  id: 20
+  run_id: 791
+  runner_id: 1
+  repo_id: 4
+  owner_id: 1
+  commit_sha: c2d72f548424103f01ee1dc02889c1e2bff816b0
+  storage_path: "26/20/1712348022423431524.chunk"
+  file_size: 1024
+  file_compressed_size: 1024
+  content_encoding: ""
+  artifact_path: "xyz/def.txt"
+  artifact_name: "multi-file-download"
+  status: 2
+  created_unix: 1712348022
+  updated_unix: 1712348022
+  expired_unix: 1720124022
+
+-
+  id: 22
+  run_id: 792
+  runner_id: 1
+  repo_id: 4
+  owner_id: 1
+  commit_sha: c2d72f548424103f01ee1dc02889c1e2bff816b0
+  storage_path: "27/5/1730330775594233150.chunk"
+  file_size: 1024
+  file_compressed_size: 1024
+  content_encoding: "application/zip"
+  artifact_path: "artifact-v4-download.zip"
+  artifact_name: "artifact-v4-download"
+  status: 2
+  created_unix: 1730330775
+  updated_unix: 1730330775
+  expired_unix: 1738106775