enhance(cache): scope cache entries by ref like GitHub (#1361)

Cache entries were only scoped by repository, so an entry a pull request saved could be restored on the default branch, for example through a `restore-keys` prefix.

Entries now carry the ref of the job that saved them. As on GitHub ([Restrictions for accessing a cache](https://docs.github.com/en/actions/reference/workflows-and-actions/dependency-caching#restrictions-for-accessing-a-cache)), a job restores entries of its own ref first, then of its pull request's base branch, then of the default branch. Pull request events are scoped by their pull request number.

Entries saved before this change are no longer restored and expire through `cache.retention`, so caches start cold once after the upgrade. Runners sharing a cache, and an external `cache-server`, should be upgraded together.

Co-authored-by: silverwind <[email protected]>
Co-authored-by: silverwind <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1361
Reviewed-by: silverwind <[email protected]>
Co-authored-by: JorgeDLMV <[email protected]>

act/artifactcache/handler_v2_test.go

@@ -231,6 +231,24 @@ func TestCacheServiceV2Lookups(t *testing.T) {
 		got := v2Call(t, handler, otherClient, "GetCacheEntryDownloadURL", map[string]any{"key": "deps-abc", "version": "v1"})
 		assert.Equal(t, false, got["ok"])
 	})
+
+	t.Run("each ref saves and restores its own entry for the same key", func(t *testing.T) {
+		clients := map[string]*http.Client{"x": testClient}
+		for _, ref := range []string{"y", "z"} {
+			handler.RegisterJob(ref, JobCredential{Repo: testRepo, Ref: "refs/pull/" + ref + "/head"})
+			clients[ref] = &http.Client{Transport: &bearerTransport{token: ref}}
+			created := v2Call(t, handler, clients[ref], "CreateCacheEntry", map[string]any{"key": "deps-abc", "version": "v1"})
+			require.Equal(t, true, created["ok"])
+			require.Equal(t, http.StatusCreated, putBlob(t, created["signed_upload_url"].(string), []byte(ref)))
+		}
+		for _, ref := range []string{"y", "z"} {
+			require.Equal(t, true, v2Call(t, handler, clients[ref], "FinalizeCacheEntryUpload", map[string]any{"key": "deps-abc", "version": "v1", "size_bytes": 1})["ok"])
+		}
+		for content, client := range clients {
+			got := v2Call(t, handler, client, "GetCacheEntryDownloadURL", map[string]any{"key": "deps-abc", "version": "v1"})
+			assert.Equal(t, content, string(getURL(t, got["signed_download_url"].(string))))
+		}
+	})
 }
 
 func TestCacheServiceV2RefusalsAreTwirp(t *testing.T) {