feat: add codecov-action flags (#545)

## PR Checklist

- [x] Addresses an existing open issue: fixes #544
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/template-typescript-node-package/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/template-typescript-node-package/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

Adds `flags: ...` to each of the three test workflows.

Author: JoshuaKGoldberg

.github/workflows/hydrate.yml

@@ -10,6 +10,7 @@ jobs:
         uses: codecov/codecov-action@v3
         with:
           files: coverage-hydrate/lcov.info
+          flags: hydrate
       - name: Archive code coverage results
         uses: actions/upload-artifact@v3
         with:

.github/workflows/setup.yml

@@ -10,6 +10,7 @@ jobs:
         uses: codecov/codecov-action@v3
         with:
           files: coverage-setup/lcov.info
+          flags: setup
       - name: Archive code coverage results
         uses: actions/upload-artifact@v3
         with:

.github/workflows/test.yml

@@ -7,6 +7,8 @@ jobs:
       - run: pnpm run test --coverage
       - name: Codecov
         uses: codecov/codecov-action@v3
+        with:
+          flags: unit
       - name: Archive code coverage results
         uses: actions/upload-artifact@v3
         with: