chore: update release scripts

[Garmelon]

Fixes some bugs I noticed during the release process, and adapts the scripts to changes in some downstream repos.

[mathlib-lean-pr-testing]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase c462e4333acaffe809774b4d9ed57878342caf92 --onto 2cd98639c40d2d2a026dd599093b70f55f55ffaf. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-27 18:03:03)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase c462e4333acaffe809774b4d9ed57878342caf92 --onto c47a0c7cf035381a2bcdd4cdf2442782eb4a5214. You can force Mathlib CI using the force-mathlib-ci label. (2026-05-29 17:08:18)

[leanprover-bot]

Reference manual CI status:

• ❗ Reference manual CI will not be attempted unless your PR branches off the nightly-with-manual branch. Try git rebase c462e4333acaffe809774b4d9ed57878342caf92 --onto 803553a556fd82fa1060efb0c43eda542130cb16. You can force reference manual CI using the force-manual-ci label. (2026-05-27 18:03:05)