build-unit-test-docker: update-alternatives for clang-apply-replacements

Meson expects a `clang-apply-replacements` implementation in order to
generate the `clang-tidy-fix` target[1,2].  With clang-21, it seems
that this moved to a versioned implementation, so we need to include it
in the `update-alternatives` invocation.

[1]: https://github.com/mesonbuild/meson/blob/3708730dee5049eca7e497629d25629534ea4964/mesonbuild/backend/ninjabackend.py#L3907
[2]: https://github.com/mesonbuild/meson/blob/3708730dee5049eca7e497629d25629534ea4964/mesonbuild/environment.py#L320

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I7d3099ac7cd675755131a1385f4ce0fc15dc55f7
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index fc68b29..6ff7c8e 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -971,6 +971,8 @@
 RUN update-alternatives --install /usr/bin/clang clang /usr/bin/clang-21 1000 \
   --slave /usr/bin/clang++ clang++ /usr/bin/clang++-21 \
   --slave /usr/bin/clang-tidy clang-tidy /usr/bin/clang-tidy-21 \
+  --slave /usr/bin/clang-apply-replacements clang-apply-replacements \
+        /usr/bin/clang-apply-replacements-21 \
   --slave /usr/bin/clang-format clang-format /usr/bin/clang-format-21 \
   --slave /usr/bin/run-clang-tidy run-clang-tidy.py \
         /usr/bin/run-clang-tidy-21 \