fix: convert H4 to H2 for accessibility

[helms-charity]

Issue

Fixes #254

Description

Blog left nav headers were failing lighthouse score when they were H4, so now they are H2 and styles were applied.

Changed Lighthouse score no longer failing for the H4s.

Test URLs

• Before (Changes from main): https://main--merative2--hlxsites.hlx.page/blog
• After (Changes from this PR): https://254-filters-h4--merative2--hlxsites.hlx.page/blog

Testing Instruction

See pagespeed.web.dev/analysis/https-www-merative-com-blog/tqt3056ejx?form_factor=mobile for the before,

pagespeed.web.dev/analysis/https-254-filters-h4--merative2--hlxsites-hlx-page-blog/uer9rayiay?form_factor=mobile for after.

Also, selection filters should display a count in Mobile.

[aem-code-sync[bot]]

Hello, I'm Franklin Bot and I will run some test suites that validate the page speed. In case there are problems, just click the checkbox below to rerun the respective action.

• [ ] Re-run PSI Checks

[aem-code-sync[bot]]

Page	Scores	Audits	Google
/blog

[aem-code-sync[bot]]

Page	Scores	Audits	Google
/blog

[helms-charity]

@proeung Thank you! I knew I had to do that, then I got distracted and forgot....

[aem-code-sync[bot]]

Page	Scores	Audits	Google
/blog

[aem-code-sync[bot]]

Page	Scores	Audits	Google
/blog