Fix mojibake

[akhenry]

Closes #5884

Describe your changes:

Modifies the build process to prepend the generated theme CSS files with explicit UTF-8 encoding. In testing this seems to fix the mojibake issue.

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• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Is this change backwards compatible? For example, developers won't need to change how they are calling the API or how they've extended core plugins such as Tables or Plots.

Author Checklist

• Changes address original issue?
• Tests included and/or updated with changes?
• Command line build passes?
• Has this been smoke tested?
• Testing instructions included in associated issue OR is this a dependency/testcase change?

Reviewer Checklist

• Changes appear to address issue?
• Reviewer has tested changes by following the provided instructions?
• Changes appear not to be breaking changes?
• Appropriate automated tests included?
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• Has associated issue been labelled bug? (only applicable if this PR is for a bug fix)

[deploysentinel]

Current Playwright Test Results Summary

✅ 14 Passing

Run may still be in progress, this comment will be updated as current testing workflow or job completes...

(Last updated on 09/20/2023 08:36:31pm UTC)

Run Details

Running Workflow e2e-couchdb on Github Actions

Commit: cd56997

Started: 09/20/2023 08:29:50pm UTC

View Detailed Build Results

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Current Playwright Test Results Summary

✅ 139 Passing - ⚠️ 6 Flaky

Run may still be in progress, this comment will be updated as current testing workflow or job completes...

(Last updated on 09/20/2023 08:36:31pm UTC)

Run Details

Running Job e2e-stable on CircleCI

Commit: cd56997

Started: 09/20/2023 08:28:32pm UTC

⚠️ Flakes

📄   functional/plugins/notebook/restrictedNotebook.e2e.spec.js • 2 Flakes

Top 1 Common Error Messages

null	2 Test Cases Affected

Test Case Results

Test Case	Last 7 days Failures	Last 7 days Flakes
Restricted Notebook with a page locked and with an embed @addinit Allows embeds to be deleted if page unlocked @addinit Retry 1 • Initial Attempt	0% (0) 0 / 114 runs failed over last 7 days	43.86% (50) 50 / 114 runs flaked over last 7 days
Restricted Notebook with a page locked and with an embed @addinit Disallows embeds to be deleted if page locked @addinit Retry 1 • Initial Attempt	1.75% (2) 2 / 114 runs failed over last 7 days	36.84% (42) 42 / 114 runs flaked over last 7 days

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📄   functional/plugins/telemetryTable/telemetryTable.e2e.spec.js • 1 Flake

Test Case Results

Test Case	Last 7 days Failures	Last 7 days Flakes
Telemetry Table unpauses and filters data when paused by button and user changes bounds Retry 1 • Initial Attempt	3.64% (4) 4 / 110 runs failed over last 7 days	17.27% (19) 19 / 110 runs flaked over last 7 days

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📄   functional/plugins/plot/tagging.e2e.spec.js • 1 Flake

Test Case Results

Test Case	Last 7 days Failures	Last 7 days Flakes
Plot Tagging Tags work with Overlay Plots Retry 2 • Retry 1 • Initial Attempt	33.33% (36) 36 / 108 runs failed over last 7 days	15.74% (17) 17 / 108 runs flaked over last 7 days

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📄   functional/planning/timelist.e2e.spec.js • 1 Flake

Test Case Results

Test Case	Last 7 days Failures	Last 7 days Flakes
Time List Create a Time List, add a single Plan to it and verify all the activities are displayed with no milliseconds Retry 1 • Initial Attempt	1.37% (2) 2 / 146 runs failed over last 7 days	49.32% (72) 72 / 146 runs flaked over last 7 days

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📄   functional/plugins/notebook/notebookSnapshots.e2e.spec.js • 1 Flake

Test Case Results

Test Case	Last 7 days Failures	Last 7 days Flakes
Snapshot image tests Can drop an image onto a notebook and create a new entry Retry 1 • Initial Attempt	1.82% (1) 1 / 55 run failed over last 7 days	78.18% (43) 43 / 55 runs flaked over last 7 days

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View Detailed Build Results

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