ci(linux): remove Arch container, standardize workflows, fix credential exposure

- Remove Arch container and pacman steps from nightly/stable Linux jobs;
  all three workflows now run identically on the Ubuntu runner
- Switch gamemode install from pacman to apt in nightly/stable
- Add persist-credentials: false to Checkout CI Scripts in all three workflows

.github/workflows/build-linux.yml

@@ -97,6 +97,8 @@ jobs:
     steps:
       - name: Checkout CI Scripts
         uses: actions/checkout@v4
+        with:
+          persist-credentials: false
 
       - name: Clone Citron Source
         # No --recursive: build-citron-linux.sh uses CPM to fetch all library

.github/workflows/build_nightly.yml

@@ -349,7 +349,6 @@ jobs:
     if: needs.check-version.outputs.should_build == 'true'
     runs-on: ${{ matrix.os }}
     timeout-minutes: 120
-    container: ghcr.io/pkgforge-dev/archlinux:latest
     env:
       CPM_SOURCE_CACHE: ${{ github.workspace }}/.cpm-cache
 
@@ -374,11 +373,10 @@ jobs:
             arch_arg: ""
 
     steps:
-      - name: Install Git
-        run: pacman -Syu --noconfirm --needed git
-
       - name: Checkout CI Scripts
         uses: actions/checkout@v4
+        with:
+          persist-credentials: false
 
       - name: Clone Citron Source
         # No --recursive: build-citron-linux.sh uses CPM to fetch all library
@@ -414,11 +412,6 @@ jobs:
           restore-keys: |
             cpm-linux-${{ runner.os }}-${{ matrix.os }}-
 
-      - name: Install Packaging Dependencies
-        # package-citron-linux.sh (run by build-citron-linux.sh's package stage)
-        # bundles libgamemode.so into the AppImage if present on the system.
-        run: pacman -Syu --noconfirm --needed gamemode
-
       - name: Setup Build Environment
         working-directory: ./citron
         run: |

.github/workflows/build_stable.yml

@@ -348,7 +348,6 @@ jobs:
     if: needs.check-version.outputs.should_build == 'true'
     runs-on: ${{ matrix.os }}
     timeout-minutes: 120
-    container: ghcr.io/pkgforge-dev/archlinux:latest
     env:
       CPM_SOURCE_CACHE: ${{ github.workspace }}/.cpm-cache
 
@@ -373,11 +372,10 @@ jobs:
             arch_arg: ""
 
     steps:
-      - name: Install Git
-        run: pacman -Syu --noconfirm --needed git
-
       - name: Checkout CI Scripts
         uses: actions/checkout@v4
+        with:
+          persist-credentials: false
 
       - name: Clone Citron Source
         # No --recursive: build-citron-linux.sh uses CPM to fetch all library
@@ -413,11 +411,6 @@ jobs:
           restore-keys: |
             cpm-linux-${{ runner.os }}-${{ matrix.os }}-
 
-      - name: Install Packaging Dependencies
-        # package-citron-linux.sh (run by build-citron-linux.sh's package stage)
-        # bundles libgamemode.so into the AppImage if present on the system.
-        run: pacman -Syu --noconfirm --needed gamemode
-
       - name: Setup Build Environment
         working-directory: ./citron
         run: |