docs(nx-dev): fix inconsistent styling in SectionHeading components (#29597)

Removed the redundant "text-white" class from SectionHeading components to standardize styles.

(cherry picked from commit dc2c9da)

Author: bcabanes

nx-dev/nx-dev/pages/whitepaper-fast-ci.tsx

@@ -78,11 +78,7 @@ export function WhitePaperFastCI(): ReactElement {
                   </p>
 
                   <div className="mt-12 text-center">
-                    <SectionHeading
-                      as="p"
-                      variant="subtitle"
-                      className="text-white"
-                    >
+                    <SectionHeading as="p" variant="subtitle">
                       See how to get fast CI, built for monorepos
                     </SectionHeading>
                     <ButtonLink

nx-dev/ui-enterprise/src/lib/trial-nx-enterprise.tsx

@@ -33,7 +33,7 @@ export function TrialNxEnterprise(): ReactElement {
             </p>
 
             <div className="mt-12 text-center">
-              <SectionHeading as="p" variant="subtitle" className="text-white">
+              <SectionHeading as="p" variant="subtitle">
                 How a Proof of Value works?
               </SectionHeading>
               <ButtonLink