gh-35351: Add minimum version of conda gap package

    
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### 📚 Description

Since #35093, sage no longer builds
with gap 4.11. With this PR the new minimum version is correctly
specified for the conda installation. This currently doesn't work as
there is no suitable conda package yet, see https://github.com/conda-
forge/gap-feedstock/pull/68. However, better fail with a good error
message then some random warning during build.

It would be nice if in the future breaking package updates would only
happen if conda provides a suitable package.

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### ⌛ Dependencies
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URL: #35351
Reported by: Tobias Diez
Reviewer(s): Dima Pasechnik

build/pkgs/gap/distros/conda.txt

@@ -1 +1 @@
-gap-defaults
+gap-defaults>=4.12.2