github: Evict old entries from ccache

We don't want to build old versions using these caches, so we don't
need old entries (if header files change, there could be lots of
differences that increase the cache size unnecessarily).

.github/workflows/windows.yml

@@ -16,6 +16,7 @@ env:
   # since the compilers are newly installed every time, we have to use this to
   # avoid cache misses
   CCACHE_COMPILERCHECK: content
+  EVICT_CCACHE_AGE: 1200s
   MONOLITHIC: yes
 
 jobs:
@@ -53,6 +54,10 @@ jobs:
           ccache -sz
       - uses: ./.github/actions/default
       - run: ccache -sv
+      - if: github.event_name == 'push'
+        run: |
+          ccache --evict-older-than ${{ env.EVICT_CCACHE_AGE }}
+          ccache -sv
       # delete old cache entry as we currently can't update it any other way
       - env:
           GH_TOKEN: ${{ github.token }}
@@ -114,6 +119,10 @@ jobs:
         # sometimes streaming/threading tests hang completely
         timeout-minutes: 30
       - run: ccache -sv
+      - if: github.event_name == 'push'
+        run: |
+          ccache --evict-older-than ${{ env.EVICT_CCACHE_AGE }}
+          ccache -sv
       # delete old cache entry as we currently can't update it any other way
       - env:
           GH_TOKEN: ${{ github.token }}