[no-Jira] Add closing tag to sign-in-modal

[canac]

Description

Fixes DataDog errors like this one:

HTML tags must be properly nested and closed: <div class=modal-body> <div class=content> <sign-in-form on-success=$ctrl.onSuccess() on-failure=$ctrl.onFailure() last-purchase-id=$ctrl.lastPurchaseId on-sign-up-with-okta=$ctrl.onSignUp() on-reset-password=$ctrl.onResetPassword() /> </div> </div> 

Testing

No user-facing changes

Checklist:

• I have given my PR a title with the format "EP-(JIRA#) (summary sentence max 80 chars)"
• I have applied the appropriate labels (Add the label "On Staging" to get the branch automatically merged into staging)
• I have requested a review from another person on the project
• I have checked that stage-branch-merger successfully merged my branch to staging or manually merged it myself
• I have tested my changes in staging for regular checkout
• I have tested my changes in staging for branded checkout

[stage-branch-merger]

I see you added the "On Staging" label, I'll get this merged to the staging branch!

[wjames111]

Sorry for the late review on such a simple change!