RSE: Unittests: Update unity version to 2.6.1

The previously used Unity tag triggered a "missing-declarations" error
because the functions IsStringInBiggerString and
UnityStringArgumentMatches were used in only one source file but were
not declared as static. This issue has been resolved in the new
version.

Change-Id: I06e41ae0063eca8774e9e25be822c25c15129d9f
Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
1 file changed