fix(prow-jobs/pingcap-qe/ci): use deno task for flaky-tests reporter (#4571)
Replace direct deno script execution with a deno task that references tools/reporters/ci/flaky-tests/deno.json. Rename script_url to project_url and call `deno task run` to execute the configured task, preserving the same repo/branch/date arguments. (commit: d26d202)
