ci: Correctly parse mirrored changelog for release-please

[twishabansal]

This PR fixes the Mirror Toolbox Changelog workflow to prevent it from creating corrupted release-please pull requests.

Problems Addressed:

1. Mangled Links: The release-please parser was aggressively re-linking already-correct URLs from the mirrored changelog, creating nested and broken links.
2. Zero-Width Spaces: The source changelog contained invisible characters (as ​) that were breaking the initial parsing of the links.

The Fixes:

• The script now performs a two-step process on the changelog links:
  1. It first cleans the input by removing the ​ HTML entity.
  2. It then protects the output by inserting an invisible Unicode zero-width space (\u200B) into the link text (e.g., [toolbox#​1234]). This breaks the release-please parser's pattern matching without affecting the visual appearance.

Output

Override message:

Release please content:

### Features

* **sources/mysql:** postgres3([genai-toolbox#​1707](https://github.com/googleapis/genai-toolbox/issues/1707)) ([eeb694c](https://github.com/googleapis/genai-toolbox/commit/eeb694c20facc40a38bfa67073c4cb1f3dd657ff)) ([7e14f8d](https://github.com/gemini-cli-extensions/cloud-sql-postgresql-observability/commit/7e14f8d4701b3ffb5ffd3970ac0a9ed86625c088))
* **sources/postgres4:** Escape program_name for MySQL ([genai-toolbox#​1717](https://github.com/googleapis/genai-toolbox/issues/1717)) ([02f7f8a](https://github.com/googleapis/genai-toolbox/commit/02f7f8af979057efe99fd138cb1b958130355b68)) ([7e14f8d](https://github.com/gemini-cli-extensions/cloud-sql-postgresql-observability/commit/7e14f8d4701b3ffb5ffd3970ac0a9ed86625c088))
* **tools/postgres2:** Ts. ([genai-toolbox#​1673](https://github.com/googleapis/genai-toolbox/issues/1673)) ([089081f](https://github.com/googleapis/genai-toolbox/commit/089081feb0e32f9eb65d00df5987392d413a4081)) ([7e14f8d](https://github.com/gemini-cli-extensions/cloud-sql-postgresql-observability/commit/7e14f8d4701b3ffb5ffd3970ac0a9ed86625c088))
* **tools/postgres5:** Allow 2xx status code on tool invocation ([genai-toolbox#​1761](https://github.com/googleapis/genai-toolbox/issues/1761)) ([a06d0d8](https://github.com/googleapis/genai-toolbox/commit/a06d0d8735fbec29bea97457248845a8c6b4aa3c)) ([7e14f8d](https://github.com/gemini-cli-extensions/cloud-sql-postgresql-observability/commit/7e14f8d4701b3ffb5ffd3970ac0a9ed86625c088))
* postges random 1([genai-toolbox#​1770](https://github.com/googleapis/genai-toolbox/issues/1770)) ([eaf7740](https://github.com/googleapis/genai-toolbox/commit/eaf77406fd386c12315d67eb685dc69e0415c516)) ([7e14f8d](https://github.com/gemini-cli-extensions/cloud-sql-postgresql-observability/commit/7e14f8d4701b3ffb5ffd3970ac0a9ed86625c088))