sagemathgh-37726: sage-bootstrap: update cryptographic hashes

    
<!-- ^ Please provide a concise and informative title. -->
<!-- ^ Don't put issue numbers in the title, do this in the PR
description below. -->
<!-- ^ For example, instead of "Fixes sagemath#12345" use "Introduce new method
to calculate 1 + 2". -->
<!-- v Describe your changes below in detail. -->
<!-- v Why is this change required? What problem does it solve? -->
<!-- v If this PR resolves an open issue, please link to it here. For
example, "Fixes sagemath#12345". -->

Update cryptographic hashes to use sha256 instead of sha1 due to
insecurity of sha1.

- Fixes sagemath#37691
- Fixes sagemath#37558, see also
sagemath#36677 (comment)

### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. -->

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation accordingly.

### ⌛ Dependencies

<!-- List all open PRs that this PR logically depends on. For example,
-->
<!-- - sagemath#12345: short description why this is a dependency -->
<!-- - sagemath#34567: ... -->

- sagemath#37570
- sagemath#37249
- sagemath#37914
    
URL: sagemath#37726
Reported by: Faisal
Reviewer(s): Matthias Köppe, roed314