support/testing: TestPythonPy3Incremental: update expected string

Since python-incremental 24.7.0, there is no longer a dot before an rc
specifier [1].

Update TestPythonPy3Incremental expected result to
"[package, version 1.2.3rc4]".

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/8199992642

[1] https://github.com/twisted/incremental/commit/d482dfff3f1c18eed69372937958c3f2481f6252

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Julien Olivain <ju.o@free.fr>

support/testing/tests/package/sample_python_incremental.py

@@ -1,3 +1,3 @@
 import incremental
 v = incremental.Version("package", 1, 2, 3, release_candidate=4)
-assert(str(v) == "[package, version 1.2.3.rc4]")
+assert(str(v) == "[package, version 1.2.3rc4]")