TestDirHash & TestDirHashWithSymlink unit test on CI fails on window runner

[manzil-infinity180]

Currently, the unit tests TestDirHash and TestDirHashWithSymlink fail on Windows CI runners.
The tests are being temporarily skipped using a go build flag, but the goal is to fix and re-enable them to ensure cross-platform consistency.
References
PR: #583

=== RUN   TestDirHash
    file_test.go:98: 
        	Error Trace:	D:/a/go-witness/go-witness/attestation/file/file_test.go:98
        	Error:      	Not equal: 
        	            	expected: ""
        	            	actual  : "ba9842eac063209c5f67c5a202b2b3a710f8f845f1d064f54af56763645b895b"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-
        	            	+ba9842eac063209c5f67c5a202b2b3a710f8f845f1d064f54af56763645b895b
        	Test:       	TestDirHash
--- FAIL: TestDirHash (0.00s)
=== RUN   TestDirHashWithSymlink
    file_test.go:131: 
        	Error Trace:	D:/a/go-witness/go-witness/attestation/file/file_test.go:131
        	Error:      	Not equal: 
        	            	expected: ""
        	            	actual  : "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-
        	            	+e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
        	Test:       	TestDirHashWithSymlink
--- FAIL: TestDirHashWithSymlink (0.00s)