[chore] correctly escape . characters during release preparation

[mowies]

Description

This PR fixes an issue where the . character in a version string (e.g. 1.2.3) was interpreted by sed as any character and therefore needed to be properly escaped. This happened during the prepare-release workflow.
The version string for the current stable and current beta version strings provided at pipeline start is replaced as follows:

1.2.3 -> 1[.]2[.]3

This ensures that sed searches for the literal . character instead of interpreting it as a wildcard character.
I specifically used the [] syntax to avoid the hassle of "how many backslashes do i need until it's properly escaped?". (and that for bash and sed, which work different on different OSes anyways which makes it hard to test as well)

Link to tracking issue

Fixes #23981

Notes

This PR uses the same solution as done in open-telemetry/opentelemetry-collector#10631 to fix the same issue in that repo.

[evan-bradley]

Ran a quick local test just to verify, looks good to me.