CI: Use julia-actions/cache in the build-mylib job (#971)

Author: DilumAluthge

.github/workflows/ci.yml

@@ -121,6 +121,7 @@ jobs:
       - uses: julia-actions/setup-julia@9b79636afcfb07ab02c256cede01fe2db6ba808c # v2.6.0
         with:
           version: '1'
+      - uses: julia-actions/cache@824243901fb567ccb490b0d0e2483ccecde46834 # v2.0.5
       - uses: julia-actions/julia-buildpkg@90dd6f23eb49626e4e6612cb9d64d456f86e6a1c # v1.6.0
         with:
           project: 'examples/MyLib'