Fix typo found in issue board sidebar milestone dropdown

What does this MR do?

Fix typo from Assignees milestone to Assign milestone

Are there points in the code the reviewer needs to double check?

Shouldn't be

Why was this MR needed?

Makes the title make more sense

Screenshots (if relevant)

Before	After

Does this MR meet the acceptance criteria?

• Tests
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #31475 (closed)

Looks like this was first introduced in https://gitlab.com/gitlab-org/gitlab-ce/commit/6b3e3aeb9e6b78ade960a4fad1da906fa023cd5e#388a375eb575249996a70c07689a9202552a2fc2_17_25 (which IIRC, made this a typo since the first version of issue boards).

Not sure how far back we want to Pick into Stable. Will let you decide @iamphill

added frontend ~149423 labels

assigned to @iamphill

added Next Patch Release label

marked the checklist item All builds are passing as completed

marked the checklist item Conform by the merge request performance guides as completed

marked the checklist item Conform by the style guides as completed

marked the checklist item Branch has no merge conflicts with master (if it does - rebase it please) as completed

marked the checklist item Squashed related commits together as completed

Been there for months, so not really a regression.

removed Next Patch Release ~149423 labels

changed milestone to %9.2

approved this merge request

merged

mentioned in commit d031665a