added validTag string literal union

[thebinij]

Explanation

• Fixes Update ValidTag enum to string literal union type for the Text component #18867

Manual Testing Steps

No functional changes

Pre-merge author checklist

• I've clearly explained:
  • What problem this PR is solving
  • How this problem was solved
  • How reviewers can test my changes
• Sufficient automated test coverage has been added

Pre-merge reviewer checklist

• Manual testing (e.g. pull and build branch, run in browser, test code being changed)
• PR is linked to the appropriate GitHub issue
• IF this PR fixes a bug in the release milestone, add this PR to the release milestone

If further QA is required (e.g. new feature, complex testing steps, large refactor), add the Extension QA Board label.

In this case, a QA Engineer approval will be be required.

[github-actions]

CLA Signature Action: All authors have signed the CLA. You may need to manually re-run the blocking PR check if it doesn't pass in a few minutes.

[codecov]

Codecov Report

Merging #19258 (e659a6a) into develop (e7adf7a) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop   #19258      +/-   ##
===========================================
- Coverage    70.04%   70.03%   -0.01%     
===========================================
  Files          962      962              
  Lines        36875    36875              
  Branches      9468     9468              
===========================================
- Hits         25826    25824       -2     
- Misses       11049    11051       +2     

Impacted Files	Coverage Δ
ui/components/component-library/text/text.types.ts	100.00% <ø> (ø)
ui/components/component-library/text/text.tsx	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[georgewrmarshall]

Hey @thebinij, this looks great! I've just added a deprecation message to ValidTag. Thanks for your contribution