ci: Update to upload-artifact@v4

Author: qookei

.github/workflows/coverage.yml

@@ -34,7 +34,7 @@ jobs:
           ninja coverage-text
           ninja coverage-sonarqube
       - name: Upload coverage reports as artifacts
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: coverages
           path: |

.github/workflows/docs.yml

@@ -30,7 +30,7 @@ jobs:
           cd build
           ninja docs/libasync-doc
       - name: Upload docs as artifacts
-        uses: actions/upload-artifact@v2
+        uses: actions/upload-artifact@v4
         with:
           name: libasync-docs
           path: build/docs/libasync-doc/