perf: remove useless git caching from build jobs, cache gh-pages content in stage-and-check

Agent-Logs-Url: https://github.com/nextcloud/documentation/sessions/6b26cc44-eeab-4f6d-b753-625d724da038

Co-authored-by: skjnldsv <14975046+skjnldsv@users.noreply.github.com>

Author: Copilot

.github/workflows/sphinxbuild.yml

@@ -90,15 +90,6 @@ jobs:
             publish: true
 
     steps:
-      - name: Cache git metadata
-        uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
-        with:
-          path: .git
-          key: git-metadata-${{ github.sha }}
-          restore-keys: |
-            git-metadata-${{ github.sha }}
-            git-metadata
-
       - name: Checkout repository
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
@@ -141,15 +132,6 @@ jobs:
             build_pdf_path: "_build/latex"
 
     steps:
-      - name: Cache git metadata
-        uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
-        with:
-          path: .git
-          key: git-metadata-${{ github.sha }}
-          restore-keys: |
-            git-metadata-${{ github.sha }}
-            git-metadata
-
       - name: Checkout repository
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
@@ -245,15 +227,6 @@ jobs:
       additional_deployment: ${{ steps.branch.outputs.additional_deployment }}
 
     steps:
-      - name: Cache git metadata
-        uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
-        with:
-          path: .git
-          key: git-metadata-${{ github.sha }}
-          restore-keys: |
-            git-metadata-${{ github.sha }}
-            git-metadata
-
       - name: Checkout repository
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
@@ -274,18 +247,16 @@ jobs:
       # ========================================================================
       # FETCH GH-PAGES FOR LINK VALIDATION CONTEXT
       # ========================================================================
-      # We need the existing gh-pages content (old versions) so that link
-      # validation can resolve cross-version references. We use git cache
-      # to make this fast.
+      # We cache the gh-pages checkout between runs so that repeated workflow
+      # runs (e.g. on pull requests) don't have to re-fetch the full gh-pages
+      # branch every time.
       # ========================================================================
-      - name: Cache git metadata for gh-pages
+      - name: Cache gh-pages content for validation context
         uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
         with:
-          path: .git
-          key: git-metadata-${{ github.sha }}
-          restore-keys: |
-            git-metadata-${{ github.sha }}
-            git-metadata
+          path: validation-context/
+          key: gh-pages-content-${{ github.run_id }}
+          restore-keys: gh-pages-content-
 
       - name: Checkout gh-pages branch for validation context
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
@@ -424,15 +395,6 @@ jobs:
       pull-requests: write
 
     steps:
-      - name: Cache git metadata
-        uses: actions/cache@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5.0.4
-        with:
-          path: .git
-          key: git-metadata-${{ github.sha }}
-          restore-keys: |
-            git-metadata-${{ github.sha }}
-            git-metadata
-
       - name: Checkout gh-pages branch
         uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with: