[lld-macho] Fix category merging sed issue (#112955)

Fix 'sed' spacing to ensure compatibility with all platforms. 

Original failure:
https://lab.llvm.org/buildbot/#/builders/190/builds/7903
```
RUN: at line 33: sed -E '/^__OBJC_\$_CATEGORY_MyBaseClass_\$_Category01:/ { n; s/^[ \t]*\.quad[ \t]+l_OBJC_CLASS_NAME_$/\t.quad\tL_OBJC_IMAGE_INFO+3/ }' merge_cat_minimal.s > merge_cat_minimal_bad_name.s
+ sed -E '/^__OBJC_\$_CATEGORY_MyBaseClass_\$_Category01:/ { n; s/^[ \t]*\.quad[ \t]+l_OBJC_CLASS_NAME_$/\t.quad\tL_OBJC_IMAGE_INFO+3/ }' merge_cat_minimal.s
sed: 1: "/^__OBJC_\$_CATEGORY_My ...": bad flag in substitute command: '}'
```

Author: alx32

lld/test/MachO/objc-category-merging-minimal.s

@@ -30,7 +30,7 @@
 
 ############ Test merging skipped due to invalid category name ############
 # Modify __OBJC_$_CATEGORY_MyBaseClass_$_Category01's name to point to L_OBJC_IMAGE_INFO+3
-# RUN: sed -E '/^__OBJC_\$_CATEGORY_MyBaseClass_\$_Category01:/ { n; s/^[ \t]*\.quad[ \t]+l_OBJC_CLASS_NAME_$/\t.quad\tL_OBJC_IMAGE_INFO+3/ }' merge_cat_minimal.s > merge_cat_minimal_bad_name.s
+# RUN: sed -E '/^__OBJC_\$_CATEGORY_MyBaseClass_\$_Category01:/ { n; s/^[ \t]*\.quad[ \t]+l_OBJC_CLASS_NAME_$/\t.quad\tL_OBJC_IMAGE_INFO+3/}' merge_cat_minimal.s > merge_cat_minimal_bad_name.s
 
 # Assemble the modified source
 # RUN: llvm-mc -filetype=obj -triple=arm64-apple-macos -o merge_cat_minimal_bad_name.o merge_cat_minimal_bad_name.s