Bugfix: Switch Host-Based Test DSC MSVC FLAG from \GS- to /GS- (#633)

## Description

\GS- should be /GS-

- [x] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

Tested on Q35

## Integration Instructions

N/A

UnitTestFrameworkPkg/UnitTestFrameworkPkgHost.dsc.inc

@@ -25,7 +25,7 @@
 
 [BuildOptions]
 # MU_CHANGE [BEGIN] - Add build flag to detect when building host-based unit tests
-  MSFT:*_*_*_CC_FLAGS  = -D HOST_UNIT_TEST_BUILD=1 \GS- # Disable Stack Protection for Host-Based Unit Tests
+  MSFT:*_*_*_CC_FLAGS  = -D HOST_UNIT_TEST_BUILD=1 /GS- # Disable Stack Protection for Host-Based Unit Tests
   GCC:*_*_*_CC_FLAGS   = -D HOST_UNIT_TEST_BUILD=1 -fno-stack-protector # Disable Stack Protection for Host-Based Unit Tests
   XCODE:*_*_*_CC_FLAGS = -D HOST_UNIT_TEST_BUILD=1
 # MU_CHANGE [END] - Add build flag to detect when building host-based unit tests