ci: remove @semantic-release/git and @semantic-release/changelog plugins

These plugins push commits directly to main, which conflicts with
branch protection rules (PR required, signed commits). The tag and
GitHub Release are created via API by @semantic-release/github
and don't need push access.

.releaserc.json

@@ -30,16 +30,9 @@
         ]
       }
     }],
-    ["@semantic-release/changelog", {
-      "changelogFile": "CHANGELOG.md"
-    }],
     ["@semantic-release/npm", {
       "npmPublish": false
     }],
-    ["@semantic-release/git", {
-      "assets": ["package.json", "package-lock.json", "CHANGELOG.md"],
-      "message": "chore(release): ${nextRelease.version} [skip ci]\n\n${nextRelease.notes}"
-    }],
     ["@semantic-release/github", {
       "successComment": false,
       "failTitle": false