feat(#22): update Codecov only after push to main branch

.github/workflows/codecov.yaml

@@ -4,9 +4,6 @@ on:
   push:
     branches:
       - main
-  pull_request:
-    branches:
-      - main
 jobs:
   codecov:
     name: Upload coverage reports to Codecov

README.md

@@ -4,7 +4,7 @@
 [![License](https://img.shields.io/badge/license-MIT-green.svg)](https://github.com/volodya-lombrozo/jtcop/blob/main/LICENSE.txt)
 [![Hits-of-Code](https://hitsofcode.com/github/volodya-lombrozo/jtcop?branch=main&label=Hits-of-Code)](https://hitsofcode.com/github/volodya-lombrozo/jtcop/view?branch=main&label=Hits-of-Code)
 ![Lines of code](https://img.shields.io/tokei/lines/github/volodya-lombrozo/jtcop?branch=main&label=Lines-of-Code)
-
+[![codecov](https://codecov.io/gh/volodya-lombrozo/jtcop/branch/main/graph/badge.svg)](https://codecov.io/gh/volodya-lombrozo/jtcop)
 
 Almost each project uses unit tests in its codebase. It is important to have a
 common pattern of naming all that tests, because otherwise the project and tests