Duplicate Changelog Entries for Merged Branches
### Description

Somehow I end up with duplicate changelog entries after merging a MR.
E.g. 
```markdown
## v0.1.2 (2022-05-02)

### Fix

- **release**: do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH
- **release**: do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH
- **release**: try to not escape $CI_DEFAULT_BRANCH default value
- **release**: do not run run bump_version/dry_run in tag pipeline
```



### Steps to reproduce

Use gitlab and add some commits to a new branch.
Open a MR and merge it.
Run commitizen on the main branch and get a changelog with duplicated entries.


### Current behavior

Duplicate Changelog Entries:
```markdown
## v0.1.2 (2022-05-02)

### Fix

- **release**: do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH
- **release**: do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH
- **release**: try to not escape $CI_DEFAULT_BRANCH default value
- **release**: do not run run bump_version/dry_run in tag pipeline
```

### Desired behavior

No duplicates from merging a MR:
```markdown
## v0.1.2 (2022-05-02)

### Fix

- **release**: do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH
- **release**: try to not escape $CI_DEFAULT_BRANCH default value
- **release**: do not run run bump_version/dry_run in tag pipeline
```

### Screenshots

Problem appears to be that commitizen seems to parse the commit body also?!

Git log shows:
```bash
Date:   Mon May 2 15:28:31 2022 +0200

    Merge branch 'fix/improve_release_jobs' into 'master'

    fix(release): do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH

    Closes #4

    See merge request group/ci_templates!10

Date:   Mon May 2 15:12:10 2022 +0200

    fix(release): do version bump on $RELEASE_BRANCH (if defined) else on $CI_DEFAULT_BRANCH

    else dry run version bump
...
```

### Environment

Commitizen Version: 2.24.0
Python Version: 3.8.10 (tags/v3.8.10:3d8993a, May  3 2021, 11:48:03) [MSC v.1928 64 bit (AMD64)]
Operating System: Windows


Thanks for the nice tool. 😃 
diff --git a/commitizen/cz/conventional_commits/conventional_commits.py b/commitizen/cz/conventional_commits/conventional_commits.py
index 248df0f3..285f2c14 100644
--- a/commitizen/cz/conventional_commits/conventional_commits.py
+++ b/commitizen/cz/conventional_commits/conventional_commits.py
@@ -38,6 +38,7 @@ class ConventionalCommitsCz(BaseCommitizen):
         "refactor": "Refactor",
         "perf": "Perf",
     }
+    changelog_pattern = defaults.bump_pattern
 
     def questions(self) -> Questions:
         questions: Questions = [
diff --git a/tests/commands/test_changelog_command.py b/tests/commands/test_changelog_command.py
index 3f90800e..e3c4a566 100644
--- a/tests/commands/test_changelog_command.py
+++ b/tests/commands/test_changelog_command.py
@@ -872,3 +872,21 @@ def test_changelog_from_rev_latest_version_dry_run(
     out, _ = capsys.readouterr()
 
     file_regression.check(out, extension=".md")
+
+
+@pytest.mark.usefixtures("tmp_commitizen_project")
+def test_invalid_subject_is_skipped(mocker, capsys):
+    """Fix #510"""
+    non_conformant_commit_title = (
+        "Merge pull request #487 from manang/master\\n\\n"
+        "feat: skip merge messages that start with Pull request\\n"
+    )
+    create_file_and_commit(non_conformant_commit_title)
+    create_file_and_commit("feat: a new world")
+    testargs = ["cz", "changelog", "--dry-run"]
+    mocker.patch.object(sys, "argv", testargs)
+    with pytest.raises(DryRunExit):
+        cli.main()
+    out, _ = capsys.readouterr()
+
+    assert out == ("## Unreleased\\n\\n### Feat\\n\\n- a new world\\n\\n")
['tests/commands/test_changelog_command.py', 'commitizen/cz/conventional_commits/conventional_commits.py']