ci: upgrade actions/cache@v3 to v4

Upgrade the "cache" action to address the CI warning:

"""
The following actions uses Node.js version which is deprecated and
will be forced to run on node20: actions/cache@v3. For more info: [1]
"""

Link: https://github.blog/changelog/2024-03-07-github-actions-all-actions-will-run-on-node20-instead-of-node16-by-default/ [1]
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>

.github/workflows/ci.yml

@@ -59,7 +59,7 @@ jobs:
     container: jforissier/optee_os_ci
     steps:
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: builds-cache-${{ github.sha }}
@@ -281,7 +281,7 @@ jobs:
       - name: Remove /__t/*
         run: rm -rf /__t/*
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: qemuv7_check-cache-${{ github.sha }}
@@ -317,7 +317,7 @@ jobs:
       - name: Remove /__t/*
         run: rm -rf /__t/*
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: qemuv8_check-cache-${{ github.sha }}
@@ -360,7 +360,7 @@ jobs:
       - name: Remove /__t/*
         run: rm -rf /__t/*
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: qemuv8_xen_check-cache-${{ github.sha }}
@@ -396,7 +396,7 @@ jobs:
       - name: Remove /__t/*
         run: rm -rf /__t/*
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: qemuv8_xen_ffa_check-cache-${{ github.sha }}
@@ -432,7 +432,7 @@ jobs:
       - name: Remove /__t/*
         run: rm -rf /__t/*
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: qemuv8_hafnium_check-cache-${{ github.sha }}
@@ -468,7 +468,7 @@ jobs:
       - name: Remove /__t/*
         run: rm -rf /__t/*
       - name: Restore build cache
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: /github/home/.cache/ccache
           key: qemuv8_check_bti_mte_pac-cache-${{ github.sha }}