Fix to_timestamps truncated subsecond calculation

[davidwendt]

Description

Fix truncated subsecond calculation to adjust for the actual digits read in decimal 10 notation.
Added new test strings to include an appended 'Z' after the subsecond digits to test this fix.

Closes #11350

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[davidwendt]

This reminds me of quote from Young Frankenstein where Dr. Frankenstein is reading his grandfather's notes just before he shouts "It could work!" The solution he found was to change the poles from plus to minus and

[codecov]

Codecov Report

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[PointKernel]

LGTM

[davidwendt]

@gpucibot merge