.github: pass env variables explicitly as string

Since Kernel 5.10, Github Actions simply stopped working.
What happens is that `KV_MAIN` gets passed as environmental variable to
the inline script, but not as string but float, because it contains `.`.
Apparently the last digit of the misinterpreted float number is
afterwards simply dropped by YAML parsing library used by GA.
As a result, `KV_MAIN` becomes `5.1` instead of `5.10`, `versionMain`
becomes simply `5.10`, not `5.10.6`. Then in the next steps,
both `VERSION_NEW` and `VERSION_OLD` become `5.10`, and the script
thinks it is already the latest version, so simply does not create a new
pull request.

It was not an issue when Kernel version is <= 5.9, because no digit
got dropped from the variable. Now the hidden issue was uncovered.

Simply set `KV_MAIN` or others explicitly as strings, by adding quotes,
to avoid such issues.

sdk_container/src/third_party/coreos-overlay/.github/workflows/go-releases-main.yml

@@ -13,7 +13,7 @@ jobs:
       - name: Fetch latest Go release
         id: fetch-latest-release
         env:
-          GO_VERSION: 1.15
+          GO_VERSION: "1.15"
         run: |
           git clone --depth=1 --no-checkout https://github.com/golang/go
           versionMain=$(git -C go ls-remote --tags origin | cut -f2 | sed -n "/refs\/tags\/go${GO_VERSION}.[0-9]*$/s/^refs\/tags\/go//p" | egrep -v -e '(beta|rc)' | sort -ruV | head -1)

sdk_container/src/third_party/coreos-overlay/.github/workflows/kernel-releases-main.yml

@@ -13,7 +13,7 @@ jobs:
       - name: Fetch latest Kernel release
         id: fetch-latest-release
         env:
-          KV_MAIN: 5.10
+          KV_MAIN: "5.10"
         run: |
           git clone --depth=1 --no-checkout https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git linux
           versionMain=$(git -C linux ls-remote --tags origin | cut -f2 | sed -n "/refs\/tags\/v${KV_MAIN}.[0-9]*$/s/^refs\/tags\/v//p" | sort -ruV | head -1)