chore(renovate): add .tf files to scan renovate versions

as demonstrated in
https://github.com/leiicamundi/camunda-tf-rosa/pull/1/files#diff-52f738d5ac61a0e93b2cded6453409d55e0d0c9ac37da82d1a8050bdfabf3dac,
this parameter is needed to have renovate upgrading dependencies
referenced in tf modules

default.json5

@@ -109,6 +109,7 @@
         "\.yml",
         "\.sh",
         "\.go",
+        "\.tf",
         "\.tool-versions$",
         "^justfile$"
         ],