make strip: include scalar

When Scalar was made a canonical part of Git in 7b5c93c (scalar:
include in standard Git build & installation, 2022-09-02), it was added
to all relevant Makefile targets except for the `strip` target.

Let's correct that.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

Makefile

@@ -2565,7 +2565,7 @@ please_set_SHELL_PATH_to_a_more_modern_shell:
 
 shell_compatibility_test: please_set_SHELL_PATH_to_a_more_modern_shell
 
-strip: $(PROGRAMS) git$X
+strip: $(PROGRAMS) git$X scalar$X
 	$(STRIP) $(STRIP_OPTS) $^
 
 ### Target-specific flags and dependencies