fix(NcListItem): decrease font-weight, restore contrast color for subname

[Antreesy]

☑️ Resolves

• Fix regression from recent component rework (subname color was max-contrast)
• Decrease font-weight from bold 700 to medium 500
  • Numeric value is used because linter complained about it (see https://developer.mozilla.org/en-US/docs/web/css/font-weight#common_weight_name_mapping)

🖼️ Screenshots

🏚️ Before	🏡 After
Talk	--

🏁 Checklist

• ⛑️ Tests are included or are not applicable
• 📘 Component documentation has been extended, updated or is not applicable
• 3️⃣ Backport to next requested with a Vue 3 upgrade

[jancborchardt]

Looks very nice! :)

[szaimen]

Great :)

[GretaD]

works well on mail

[susnux]

/backport to next

[backportbot]

The backport to next failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout next
git pull origin next

# Create the new backport branch
git checkout -b backport/5421/next

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 585b5202

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/5421/next

Error: No changes found in backport branch

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.