chore: consolidate semver git-submodule renovate rules

[Copilot]

Addresses feedback from #3570 to reduce duplication in renovate configuration for GNOME extension git-submodules.

Changes

• Consolidated three separate rules for ubuntu/gnome-shell-extension-appindicator, GSConnect/gnome-shell-extension-gsconnect, and eonpatapon/gnome-shell-extension-caffeine into a single rule with multiple matchPackagePatterns
• All three extensions share identical configuration: matchManagers: ["git-submodules"], versioning: "semver", automerge: false
• Kept micheleg/dash-to-dock as separate rule (uses custom regex versioning)

Before (3 rules, 24 lines):

{
  "matchManagers": ["git-submodules"],
  "matchPackagePatterns": ["ubuntu/gnome-shell-extension-appindicator"],
  "versioning": "semver",
  "automerge": false
},
{
  "matchManagers": ["git-submodules"],
  "matchPackagePatterns": ["GSConnect/gnome-shell-extension-gsconnect"],
  "versioning": "semver",
  "automerge": false
},
{
  "matchManagers": ["git-submodules"],
  "matchPackagePatterns": ["eonpatapon/gnome-shell-extension-caffeine"],
  "versioning": "semver",
  "automerge": false
}

After (1 rule, 10 lines):

{
  "matchManagers": ["git-submodules"],
  "matchPackagePatterns": [
    "ubuntu/gnome-shell-extension-appindicator",
    "GSConnect/gnome-shell-extension-gsconnect",
    "eonpatapon/gnome-shell-extension-caffeine"
  ],
  "versioning": "semver",
  "automerge": false
}

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