[openwrt/openwrt] CI: kernel: Cache external toolchain

[LEDE Commits]

ansuel pushed a commit to openwrt/openwrt.git, branch openwrt-22.03:
https://git.openwrt.org/2f9b35624d105e0f6506764ca29005165010dd3e

commit 2f9b35624d105e0f6506764ca29005165010dd3e
Author: Christian Marangi <ansuelsmth at gmail.com>
AuthorDate: Fri Sep 9 21:09:30 2022 +0200

    CI: kernel: Cache external toolchain
    
    Cache external toolchain for each target to remove load from openwrt cdn
    server and make the external toolchain setup quicker.
    
    Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
    (cherry picked from commit f522c27385d6f94e5dbcc3e84968f0e38609ff1c)
---
 .github/workflows/kernel.yml | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/kernel.yml b/.github/workflows/kernel.yml
index 05bc6ed8ee..43f843b256 100644
--- a/.github/workflows/kernel.yml
+++ b/.github/workflows/kernel.yml
@@ -102,12 +102,23 @@ jobs:
       - name: Parse toolchain file
         working-directory: openwrt
         run: |
-          TOOLCHAIN_FILE=$(curl "https://downloads.cdn.openwrt.org/snapshots/targets/${{ env.TARGET }}/${{ env.SUBTARGET }}/sha256sums" \
-            | sed -n -e 's/.*\(openwrt-toolchain.*\).tar.xz/\1/p')
+          TOOLCHAIN_STRING="$(curl "https://downloads.cdn.openwrt.org/snapshots/targets/${{ env.TARGET }}/${{ env.SUBTARGET }}/sha256sums" \
+            | grep ".*openwrt-toolchain.*tar.xz")"
+          TOOLCHAIN_FILE=$(echo "$TOOLCHAIN_STRING" | sed -n -e 's/.*\(openwrt-toolchain.*\).tar.xz/\1/p')
+          TOOLCHAIN_SHA256=$(echo "$TOOLCHAIN_STRING" | cut -d ' ' -f 1)
 
           echo "TOOLCHAIN_FILE=$TOOLCHAIN_FILE" >> "$GITHUB_ENV"
+          echo "TOOLCHAIN_SHA256=$TOOLCHAIN_SHA256" >> "$GITHUB_ENV"
+
+      - name: Cache external toolchain
+        id: cache-external-toolchain
+        uses: actions/cache at v3
+        with:
+          path: openwrt/${{ env.TOOLCHAIN_FILE }}
+          key: ${{ env.TOOLCHAIN_FILE }}-${{ env.TOOLCHAIN_SHA256 }}
 
       - name: Download external toolchain
+        if: ${{ steps.cache-external-toolchain.outputs.cache-hit != 'true' }}
         shell: su buildbot -c "sh -e {0}"
         working-directory: openwrt
         run: |