Security update for tensorflow2

This update for tensorflow fixes the following issues:

Update to TF2 2.6.0 which fixes multiple CVEs (boo#1189423).

- Introduction of bazel6.3 and basel-skylib1.0.3 as build
dependencies.
The latter has been adapted to all a version in its package
name (if %set_ver_suffix is set to 1). This allows multiple
versions to exist for one product (not installed).
NOTE: basel-skylib1.0.3 does not exist in oS:Factory:
basel-skylib in oS:Factory - the base version - is 1.0.3.

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