gh-36781: `libbraiding`: Actually update to version 1.2
    
<!-- ^^^^^
Please provide a concise, informative and self-explanatory title.
Don't put issue numbers in there, do this in the PR body below.
For example, instead of "Fixes #1234" use "Introduce new method to
calculate 1+1"
-->
<!-- Describe your changes here in detail -->
As previously observed in #36283, the intended upgrade of libbraiding to
1.2 as part of #35380 was faulty, and as a result we have a
`libbraiding-1.2.tar.gz` on our mirrors that is actually 1.1.

Here we rectify the situation.

<!-- Why is this change required? What problem does it solve? -->
<!-- If this PR resolves an open issue, please link to it here. For
example "Fixes #12345". -->
<!-- If your change requires a documentation PR, please link it
appropriately. -->

### 📝 Checklist

<!-- Put an `x` in all the boxes that apply. -->
<!-- If your change requires a documentation PR, please link it
appropriately -->
<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
<!-- Feel free to remove irrelevant items. -->

- [x] The title is concise, informative, and self-explanatory.
- [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
- #12345: short description why this is a dependency
- #34567: ...
-->

<!-- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->
    
URL: #36781
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik

Author: Release Manager

build/pkgs/libbraiding/checksums.ini

@@ -1,5 +1,5 @@
-tarball=libbraiding-VERSION.tar.gz
-sha1=06610e47eb243b27aea0ad399b41614fcdb179c9
-md5=5466605026b90bdca7ca20852f88b5c5
-cksum=704753563
-upstream_url=https://github.com/miguelmarco/libbraiding/releases/download/1.1/libbraiding-1.1.tar.gz
+tarball=libbraiding-VERSION-actually-VERSION.tar.gz
+sha1=b7e13778784fe1e36e7c0cbd7a4c234a090cd1b2
+md5=0513967c81b783ea66336b7ad0562534
+cksum=3619705925
+upstream_url=https://github.com/miguelmarco/libbraiding/releases/download/VERSION/libbraiding-VERSION.tar.gz