Stop observing ADS while the algorithms are running

[MohamedAlmaki]

Description of work

This PR fixes a crash in the ISIS Calibration and ISIS Diagnostics tabs. The crash is caused by multiple calls to the setIndices slot, which updates the text of the plot indices line edit. This PR provides a quick solution for the release by disabling the ADS observer while running the algorithms to avoid multiple simultaneous updates.

Fixes #38078.

To test:

Follow #38078

This does not require release notes because regression bug introduced in this release

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[rbauststfc]

Changes look good. I've tested both sets of steps on the linked issue and there are no crashes. Great job getting to the bottom of this one, it sounded tricky to diagnose!