gh-36896: `src/sage/interfaces/{gap,kenzo,scilab}`: fix doctests warnings
Fix warnings like
```
File "src/sage/interfaces/gap.py", line 1509, in
sage.interfaces.gap.gap_reset_workspace
Warning: Variable 'gap' referenced here was set only in doctest marked
'# long time'
P = [Process(target=gap, args=("14242",)) for i in range(4)]
File "src/sage/interfaces/kenzo.py", line 134, in
sage.interfaces.kenzo.Sphere
Warning: Consider using a block-scoped tag by inserting the line 'sage:
# optional - kenzo' just before this line to avoid repeating the tag 4
times
from sage.interfaces.kenzo import Sphere # optional - kenzo
File "src/sage/interfaces/scilab.py", line 252, in
sage.interfaces.scilab.Scilab.set_seed
Warning: Consider using a block-scoped tag by inserting the line 'sage:
# optional - scilab' just before this line to avoid repeating the tag 4
times
from sage.interfaces.scilab import Scilab # optional - scilab
```
We also use more block scope tags.
However, we let one warning in `src/sage/interfaces/gp.py`. This is a
doctest with `# 32-bit` and `# 64-bit` tags.
```
File "src/sage/interfaces/gp.py", line 799, in
sage.interfaces.gp.Gp.new_with_bits_prec
Warning: Variable 'pi_def' referenced here was set only in doctest
marked '# needs sage.libs.pari sage.symbolic'
pi_def.precision()
```
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URL: https://github.com/sagemath/sage/pull/36896
Reported by: David Coudert
Reviewer(s): Matthias Köppe
