Change Sistering logo to use svg in volunteer navbar

[briantu]

Ticket link

Closes #125

Implementation description

• Changed Sistering logo to the svg format

Steps to test

1. Go to /volunteer/shifts or /volunteer/postings and check that the logo in the volunteer navbar is an svg

What should reviewers focus on?

• Logo and spacing look good

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR

[github-actions]

Visit the preview URL for this PR (updated for commit 9dbef8d):

https://sistering-dev--pr198-brian-use-svg-logo-i-4u558iqg.web.app

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[LenaNguyen]