Unit tests: fix coverage exclude paths on Windows

[lorjala]

Description

Govr requires forward slashed even on Windows for exclude/filter paths.

Fix for #8107.

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change

[lorjala]

@OPpuolitaival Review this.

[cmonr]

Is this the only place where path slashes might be considered a problem? Does this handle relative paths as well?

[lorjala]

@cmonr

Is this the only place where path slashes might be considered a problem?

Yes. Gcovr uses regular expressions as filters and their documentation suggest always using forward slashes.

Does this handle relative paths as well?

Yes.

[cmonr]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 3072
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/8123/

Triggering tests

/morph test
/morph export-build
/morph mbed2-build

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2685
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/8123/

[mbed-ci]

Test : SUCCESS

Build number : 2861
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/8123/2861