fix !project_id error message typo (#435)

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Small change! This error message seems like it's missing a word, so
based on the comment on line 202, I changed it
from
> `⚠️ Failed to a project ID from the given inputs.`

to

> `⚠️ Failed to compute a project ID from the given inputs`

src/main.ts

@@ -202,7 +202,7 @@ export async function run(logger: Logger) {
  // Set the project ID environment variables to the computed values.
  if (!projectID) {
  logger.info(
- `⚠️ Failed to a project ID from the given inputs. Neither the ` +
+ `⚠️ Failed to compute a project ID from the given inputs. Neither the ` +
  `"project_id" output nor any environment variables will be ` +
  `exported. If you require these values in other steps, specify the ` +
  `"project_id" input directly.`,