build.zig: poison the configure cache appropriately

Until #35473 is implemented we have to re-run configure logic in case of
these things:
* git commit changes
* test-cases on the file system changed
* test-incremental on the file system changed

build.zig

@@ -259,6 +259,11 @@ pub fn build(b: *std.Build) !void {
             std.debug.print("error: version info cannot be retrieved from git. Zig version must be provided using -Dversion-string\n", .{});
             std.process.exit(1);
         }
+
+        // Ensure git version changes get picked up
+        // https://codeberg.org/ziglang/zig/issues/35473
+        b.graph.poisonCache();
+
         const version_string = b.fmt("{d}.{d}.{d}", .{ zig_version.major, zig_version.minor, zig_version.patch });
 
         var code: u8 = undefined;

test/tests.zig

@@ -2901,6 +2901,10 @@ pub fn addCases(
 
     var cases = @import("src/Cases.zig").init(gpa, arena, io);
 
+    // Ensure changes to these files get picked up
+    // https://codeberg.org/ziglang/zig/issues/35473
+    b.graph.poisonCache();
+
     var dir = try b.root.openDir(io, "test/cases", .{ .iterate = true });
     defer dir.close(io);
 
@@ -2959,6 +2963,10 @@ pub fn addIncrementalTests(b: *std.Build, test_step: *Step, test_filters: []cons
         }),
     });
 
+    // Ensure changes to these files get picked up
+    // https://codeberg.org/ziglang/zig/issues/35473
+    b.graph.poisonCache();
+
     var dir = try b.root.openDir(io, "test/incremental", .{ .iterate = true });
     defer dir.close(io);