fix: Fix Warning messages (acts-project#3679)

Fix following messages:
```console
/__w/acts/acts/build/../CI/test_coverage.py:44: SyntaxWarning: invalid escape sequence '\d'
  map(int, re.match("gcovr (\d+\.\d+)", gcovr_version_text).group(1).split("."))
/__w/acts/acts/build/../CI/test_coverage.py:66: SyntaxWarning: invalid escape sequence '\.'
  excludes = ["-e", "../Tests/", "-e", ".*json\.hpp"]
```

CI/test_coverage.py

@@ -41,7 +41,7 @@ def call(cmd):
 
 ret, gcovr_version_text = check_output(["gcovr", "--version"])
 gcovr_version = tuple(
-    map(int, re.match("gcovr (\d+\.\d+)", gcovr_version_text).group(1).split("."))
+    map(int, re.match(r"gcovr (\d+\.\d+)", gcovr_version_text).group(1).split("."))
 )
 
 extra_flags = []
@@ -63,7 +63,7 @@ def call(cmd):
 if not os.path.exists(coverage_dir):
     os.makedirs(coverage_dir)
 
-excludes = ["-e", "../Tests/", "-e", ".*json\.hpp"]
+excludes = ["-e", "../Tests/", "-e", r".*json\.hpp"]
 
 # create the html report
 call(