downgrade bazel to 3.7.0

that's our target for now.

toolchain/BUILD.sdk.bazel

@@ -4,7 +4,8 @@ package(
     default_visibility = ["//visibility:public"],
 )
 
+# TODO(motiejus) use json.encode() and unquote these variables with bazel 4+.
 zig_build_macro(
-    absolute_path = {absolute_path},
-    zig_include_root = {zig_include_root},
+    absolute_path = "{absolute_path}",
+    zig_include_root = "{zig_include_root}",
 )

toolchain/defs.bzl

@@ -157,14 +157,13 @@ def _zig_repository_impl(repository_ctx):
             ZIG_TOOL_WRAPPER.format(zig = str(repository_ctx.path("zig")), zig_tool = zig_tool),
         )
 
-    absolute_path = json.encode(str(repository_ctx.path("")))
     repository_ctx.template(
         "BUILD.bazel",
         Label("//toolchain:BUILD.sdk.bazel"),
         executable = False,
         substitutions = {
-            "{absolute_path}": absolute_path,
-            "{zig_include_root}": json.encode(zig_include_root),
+            "{absolute_path}": str(repository_ctx.path("")),
+            "{zig_include_root}": zig_include_root,
         },
     )