ci: fix macOS/Linux configure (oakgl) and Windows MSYS2 git

- OAK_ENABLE_DYNAMIC_RENDER_BACKEND now defaults ON; it was previously
  undefined (OFF) unless passed, so CI configure failed on the
  unconditional oakgl target references in app/worker/tests
- add git to the MSYS2 package list in ci.yml and cd.yml; the OTIO
  build step runs git clone in the msys2 shell, where git is not
  installed by default

.github/workflows/ci.yml

@@ -92,6 +92,7 @@ jobs:
           update: true
           cache: true
           install: >-
+            git
             mingw-w64-ucrt-x86_64-cmake
             mingw-w64-ucrt-x86_64-ninja
             mingw-w64-ucrt-x86_64-gcc