CI (alpine): Adapt ccache size to approx. twice the size after one run.

It looks like with the update to Alpine Linux 3.20, the object files
that are produced by the compiler became smaller or the cache compression
of ccache is more efficient.
Reduce the maximum cache size to approx. twice the size of the ccache
after a single clean run.

.github/workflows/build-arch-emu.yaml

@@ -38,19 +38,19 @@ jobs:
         arch: [x86, aarch64, armv7, ppc64le, s390x, riscv64]
         include:
           - arch: x86
-            ccache-max: 80M
+            ccache-max: 64M
             extra-build-libs: ":GraphBLAS:LAGraph"
             extra-check-libs: ":GraphBLAS:LAGraph"
           - arch: aarch64
-            ccache-max: 42M
+            ccache-max: 28M
           - arch: armv7
-            ccache-max: 42M
+            ccache-max: 25M
           - arch: ppc64le
-            ccache-max: 45M
+            ccache-max: 28M
           - arch: s390x
-            ccache-max: 42M
+            ccache-max: 28M
           - arch: riscv64
-            ccache-max: 42M
+            ccache-max: 28M
 
     name: alpine (${{ matrix.arch }})