### Describe the issue

I set `axios.defaults.headers.common['Content-Type'] = 'application/json'`. When firing a `axios.patch` request (without a config), the request uses `application/x-www-form-urlencoded` instead.

### Example Code

```js
// This does not work as expected:
axios.defaults.headers.common['Content-Type'] = 'application/json'

// This does:
axios.defaults.headers.common['Content-Type'] = 'application/json'
axios.defaults.headers.patch['Content-Type'] = 'application/json'
```


### Expected behavior

I expected POST requests to use `axios.defaults.headers.common`, too.

I think this is where the problem (or intended behaviour) comes from: https://github.com/axios/axios/blob/3f53eb6960f05a1f88409c4b731a40de595cb825/lib/core/dispatchRequest.js#L46

### Axios Version

1.4.0

### Adapter Version

_No response_

### Browser

Firefox

### Browser Version

116.0.3 (64-bit)

### Node.js Version

_No response_

### OS

_No response_

### Additional Library Versions

_No response_

### Additional context/Screenshots

_No response_
test/specs/defaults.spec.js
utils.merge(defaults.headers.common, defaults.headers.get, {
          'X-COMMON-HEADER': 'commonHeaderValue',
          'X-GET-HEADER': 'getHeaderValue',
          'X-FOO-HEADER': 'fooHeaderValue',
          'X-BAR-HEADER': 'barHeaderValue'
        })
      );
      done();
    });
  });
  it('should be used by custom instance if set before instance created', function (done) {
    axios.defaults.baseURL = 'http://example.org/';
    const instance = axios.create();
    instance.get('/foo');
    getAjaxRequest().then(function (request) {
      expect(request.url).toBe('http://example.org/foo');
      done();
    });
  });
  it('should not be used by custom instance if set after instance created', function (done) {
    const instance = axios.create();
    axios.defaults.baseURL = 'http://example.org/';
    instance.get('/foo');
    getAjaxRequest().then(function (request) {
      expect(request.url).toBe('/foo');
      done();
    });
  });
});