[llvm-objcopy] [COFF] Rename a test from .yaml to .test. NFC.

Tests named .yaml aren't executed by default in this directory
(while they are within e.g. LLD).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351657 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/test/tools/llvm-objcopy/COFF/strip-all.yaml b/test/tools/llvm-objcopy/COFF/strip-all.test
similarity index 100%
rename from test/tools/llvm-objcopy/COFF/strip-all.yaml
rename to test/tools/llvm-objcopy/COFF/strip-all.test