Fix swagger docs for /repos/issues (#12069)

Co-authored-by: Lauris BH <lauris@nix.lv>

routers/api/v1/repo/issue.go

 	//   in: query
 	//   description: whether issue is open or closed
 	//   type: string
+	//   enum: [closed, open, all]
 	// - name: labels
 	//   in: query
 	//   description: comma separated list of labels. Fetch only issues that have any of this labels. Non existent labels are discarded
 	//   in: query
 	//   description: filter by type (issues / pulls) if set
 	//   type: string
+	//   enum: [issues, pulls]
 	// - name: milestones
 	//   in: query
 	//   description: comma separated list of milestone names or ids. It uses names and fall back to ids. Fetch only issues that have any of this milestones. Non existent milestones are discarded

templates/swagger/v1_json.tmpl

             "required": true
           },
           {
+            "enum": [
+              "closed",
+              "open",
+              "all"
+            ],
             "type": "string",
             "description": "whether issue is open or closed",
             "name": "state",
             "in": "query"
           },
           {
+            "enum": [
+              "issues",
+              "pulls"
+            ],
             "type": "string",
             "description": "filter by type (issues / pulls) if set",
             "name": "type",