Update MCUboot version to v1.8.0

Signed-off-by: Sherry Zhnag <sherry.zhang2@arm.com>
Change-Id: I52a344b550ab890a6a808a74b8653fa8f88e9cd6
diff --git a/tf-m-nightly-code-coverage.yaml b/tf-m-nightly-code-coverage.yaml
index a3b1819..0c82b2c 100644
--- a/tf-m-nightly-code-coverage.yaml
+++ b/tf-m-nightly-code-coverage.yaml
@@ -77,7 +77,7 @@
           description: "Name of Jenkins credential for authentication with LAVA."
       - string:
           name: 'MCUBOOT_REFSPEC'
-          default: 'TF-Mv1.4-integ'
+          default: 'v1.8.0'
           description: |
             Specify which MCUboot version to use
             refs/heads/master    : Pick up latest master