Disable upload-coverage-report workflow in CI. (#9056)

As far as I know nobody looks at these reports anyway, and lately
the codecov API has been failing for an expired certificate.

.github/workflows/tests.yml

@@ -32,44 +32,3 @@ jobs:
         run: |
           make test-group-${{ matrix.part }} NUM_SPLIT=6
         if: env.GIT_DIFF
-      - uses: actions/upload-artifact@v3
-        with:
-          name: "${{ github.sha }}-${{ matrix.part }}-coverage"
-          path: ./build/${{ matrix.part }}.profile.out
-
-  upload-coverage-report:
-    runs-on: ubuntu-latest
-    needs: tests
-    steps:
-      - uses: actions/checkout@v3
-      - uses: technote-space/get-diff-action@v6
-        with:
-          PATTERNS: |
-            **/**.go
-            "!test/"
-            go.mod
-            go.sum
-            Makefile
-      - uses: actions/download-artifact@v3
-        with:
-          name: "${{ github.sha }}-00-coverage"
-        if: env.GIT_DIFF
-      - uses: actions/download-artifact@v3
-        with:
-          name: "${{ github.sha }}-01-coverage"
-        if: env.GIT_DIFF
-      - uses: actions/download-artifact@v3
-        with:
-          name: "${{ github.sha }}-02-coverage"
-        if: env.GIT_DIFF
-      - uses: actions/download-artifact@v3
-        with:
-          name: "${{ github.sha }}-03-coverage"
-        if: env.GIT_DIFF
-      - run: |
-          cat ./*profile.out | grep -v "mode: set" >> coverage.txt
-        if: env.GIT_DIFF
-      - uses: codecov/codecov-action@v3.1.0
-        with:
-          file: ./coverage.txt
-        if: env.GIT_DIFF