oeqa/selftest: Update test after fetcher error changes

oeqa/selftest: Update test after fetcher error changes

The following poky commit:

4359ef08 base.bbclass: Use bb.fatal() instead of raising FuncFailed

changed the way the fetcher error is reported.

Previous reporting:
...Function failed: Fetcher failure for URL:...

New reporting:
...Fetcher failure for URL:...

Updating how the check is done fixes the test error and accurately
confirms the tested scenario for test_invalid_recipe_src_uri.

[YOCTO #10370]

(From OE-Core rev: 197da17dc97cef87375ae9190c6d1495e1c615b9)

Signed-off-by: Benjamin Esquivel <benjamin.esquivel@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>