Don't test Botan on MacOS for now

Homebrew decided to update the formula for Botan to support version 3.0 of the package only.

Until we update the bindings and the Windows library to match, we can't test on Mac.

.github/workflows/ci.yml

@@ -56,9 +56,9 @@ jobs:
     runs-on: macos-latest
     steps:
       - uses: actions/checkout@v1
-      - name: Download LLVM, botan and setup PATH
+      - name: Download LLVM and setup PATH
         run: |
-          brew install llvm@11 botan
+          brew install llvm@11
           echo "/usr/local/opt/llvm@11/bin" >> $GITHUB_PATH
           TMP_PATH=$(xcrun --show-sdk-path)/user/include
           echo "CPATH=$TMP_PATH" >> $GITHUB_ENV
@@ -87,11 +87,6 @@ jobs:
           cd tests/core
           make
         timeout-minutes: 10
-      - name: Vendor library tests
-        run: |
-          cd tests/vendor
-          make
-        timeout-minutes: 10
       - name: Odin internals tests
         run: |
           cd tests/internal