tests: use raw strings for regular expressions with escapes

Avoids SyntaxWarning on Python 3.8.

Differential Revision: https://phab.mercurial-scm.org/D5828

tests/hghave.py

@@ -722,7 +722,7 b' def has_fuzzywuzzy():'
 
 @check("clang-libfuzzer", "clang new enough to include libfuzzer")
 def has_clang_libfuzzer():
-    mat = matchoutput('clang --version', b'clang version (\d)')
+    mat = matchoutput('clang --version', br'clang version (\d)')
     if mat:
         # libfuzzer is new in clang 6
         return int(mat.group(1)) > 5
@@ -730,7 +730,7 b' def has_clang_libfuzzer():'
 
 @check("clang-6.0", "clang 6.0 with version suffix (libfuzzer included)")
 def has_clang60():
-    return matchoutput('clang-6.0 --version', b'clang version 6\.')
+    return matchoutput('clang-6.0 --version', br'clang version 6\.')
 
 @check("xdiff", "xdiff algorithm")
 def has_xdiff():
@@ -811,7 +811,7 b' def has_sqlite():'
         # WITH clause not supported
         return False
 
-    return matchoutput('sqlite3 -version', b'^3\.\d+')
+    return matchoutput('sqlite3 -version', br'^3\.\d+')
 
 @check('vcr', 'vcr http mocking library')
 def has_vcr():