chore: fix coverage report in 0.58 branch (backport #3315) (#3321)

* chore: fix coverage report (#3315)

origin/HEAD doesn't make sense for 0.x, this change generates a coverage report against 0.x

(cherry picked from commit e306056)

# Conflicts:
#	.circleci/config.yml

* Update .circleci/config.yml

Co-authored-by: Munir Abdinur <[email protected]>
Co-authored-by: Brett Langdon <[email protected]>

Author: 3 people

.circleci/config.yml

@@ -322,8 +322,8 @@ jobs:
       # Print tests/ report to stdout
       # DEV: "--ignore-errors" to skip over files that are missing
       - run: coverage report --ignore-errors --omit=ddtrace/
-      # Print diff-cover report to stdout (compares against origin/master)
-      - run: diff-cover --compare-branch origin/master coverage.xml
+      # Print diff-cover report to stdout (compares against origin/0.x)
+      - run: diff-cover --compare-branch origin/0.x coverage.xml
 
   build_base_venvs:
     executor: ddtrace_dev