chore(ci): exclude some crate from codecov testing

There's been many segfaults happening in tests, while running the test
coverage for this specific crate. An issue has been opened on
cargo-tarpaulin's repository:

https://github.com/xd009642/tarpaulin/issues/1749

Until this is fixed or worked around, we'll disable coverage testing for
this specific crate.

tarpaulin.toml

@@ -9,7 +9,7 @@ exclude-files = [
 ]
 workspace = true
 # sqlite crypto store is not tested otherwise because it's only activated by
-# matrix-sdk-crypto-ffi, which is excluded from testing below
+# matrix-sdk-crypto-ffi, which is excluded from testing below.
 features = "crypto-store"
 exclude = [
     # bindings
@@ -23,4 +23,6 @@ exclude = [
     # repo automation (ci, codegen)
     "uniffi-bindgen",
     "xtask",
+    # until it doesn't segfault anymore, this is excluded :(
+    "matrix-sdk-base",
 ]