Fix button placement on pipeline graph

What does this MR do?

Fixes the issue where stage-level actions are being cut off at the top. (Look at the play button next to Test below.)

Screenshots

Before After
Screen_Shot_2020-09-25_at_2.54.24_PM Screen_Shot_2020-09-25_at_3.22.06_PM

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Merge request reports

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