docs: fix broken links (#3605)

# Summary

Fix broken links.

Not found.

https://github.com/slsa-framework/slsa-github-generator/CONTRIBUTING.md
https://github.com/slsa-framework/slsa-github-generator/CHANGELOG.md

https://github.com/actions/starter-workflows/blob/main/ci/generic-generator-ossf-slsa3-publish.yml

## Testing Process


## Checklist

- [ ] Review the contributing [guidelines](./../CONTRIBUTING.md)
- [ ] Add a reference to related issues in the PR description.
- [ ] Update documentation if applicable.
- [ ] Add unit tests if applicable.
- [ ] Add changes to the [CHANGELOG](./../CHANGELOG.md) if applicable.

Signed-off-by: Shunsuke Suzuki <suzuki.shunsuke.1989@gmail.com>

.github/pull_request_template.md

@@ -8,8 +8,8 @@
 
 ## Checklist
 
-- [ ] Review the contributing [guidelines](./../CONTRIBUTING.md)
+- [ ] Review the contributing [guidelines](https://github.com/slsa-framework/slsa-github-generator/blob/main/CONTRIBUTING.md)
 - [ ] Add a reference to related issues in the PR description.
 - [ ] Update documentation if applicable.
 - [ ] Add unit tests if applicable.
-- [ ] Add changes to the [CHANGELOG](./../CHANGELOG.md) if applicable.
+- [ ] Add changes to the [CHANGELOG](https://github.com/slsa-framework/slsa-github-generator/blob/main/CHANGELOG.md) if applicable.

RELEASE.md

@@ -643,7 +643,7 @@ Update the `Supported Versions` section in [SECURITY.md](./SECURITY.md).
 Update:
 
 1. [Go builder's workflow](https://github.com/actions/starter-workflows/blob/main/ci/go-ossf-slsa3-publish.yml)
-2. [Generic generator's workflow](https://github.com/actions/starter-workflows/blob/main/ci/generic-generator-ossf-slsa3-publish.yml)
+2. [Generic generator's workflow](https://github.com/actions/starter-workflows/blob/main/ci/generator-generic-ossf-slsa3-publish.yml)
 
 ### Announce