update macos to 11

Author: hasindu2008

.github/workflows/c-cpp.yml

@@ -105,9 +105,9 @@ jobs:
       run: make clean && make CC=icc -j8 zstd=1
     - name: test zstd
       run: make test zstd=1 CC=icc
-  os_x_10:
-    name: OSX 10
-    runs-on: macos-10.15
+  os_x_11:
+    name: OSX 11
+    runs-on: macos-11
     steps:
     - uses: actions/checkout@v2
     - name: build
@@ -116,9 +116,9 @@ jobs:
       run: make test
     - name: examples
       run: make examples
-  os_x_10_zstd:
-    name: OSX 10 zstd
-    runs-on: macos-10.15
+  os_x_11_zstd:
+    name: OSX 11 zstd
+    runs-on: macos-11
     steps:
     - uses: actions/checkout@v2
     - name: install packages