Use Zig 0.16.0 in CI

I want to get a bunch of fixes and cleanups done in the short term for a
0.16.0 release. Once 0.16.0 and 0.17.0-dev start to diverge we can
consider branching and making ziglua main target zig master again.

Author: natecraddock

.github/workflows/docs.yml

@@ -27,7 +27,7 @@ jobs:
         uses: actions/configure-pages@v5
       - uses: mlugg/setup-zig@v2
         with:
-          version: master
+          version: "0.16.0"
       - run: make docs
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3

.github/workflows/tests.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Setup Zig
       uses: mlugg/setup-zig@v2
       with:
-        version: master
+        version: "0.16.0"
 
     - name: Run tests
       run: make test_zig_nightly
@@ -62,7 +62,7 @@ jobs:
     - name: Setup Zig
       uses: mlugg/setup-zig@v2
       with:
-        version: master
+        version: "0.16.0"
 
     - name: Run tests
       run: make test_cross